What's Wrong With... Revenge of the Cybermen

"Revenge? What is that?"

So said a Cyberman in the third episode of The Moonbase. Chief Hobson goes on to describe it as a feeling and the Cyberman cuts him off, stating that they know of these weaknesses, but are fortunate that they don't possess them.

Ever since their first appearance in The Tenth Planet, the Cybermen have been defined by their complete lack of emotion. They threw away their feelings along with their organic limbs and organs a long time ago. So, to associate a word like "Revenge" with the Cybermen in a story title is ridiculous.

The problem with the title may well lie with this story's complicated development.

Season 12 was planned and mostly commissioned by Barry Letts and Terrance Dicks. Jon Pertwee had been in the role of the Doctor for a hugely successful five years - longer than either of his predecessors - and there were concerns that the public might not readily take to a fourth actor in the role. Letts planned to have a much older Doctor to contrast with the dynamic Third - which is how the character of Harry Sullivan came into being. He was designed to do all the physical stuff.

To ease in the new fellow, it was decided to bring back the Daleks - Terry Nation contributing a story per season at this time anyway - and the popular Sontaran was quickly brought back.

John Lucarotti had come back onto the scene after a long absence, and Letts and Dicks had used him on their doomed Moonbase 3 series. He would contribute a space station story, and it was decided to reuse this set in another story, to be shown later in the season, as a budget-saving measure.

Fans had been asking for years about the Cybermen, not seen since The Invasion in 1968, apart from the odd cameo. They had almost featured in Frontier in Space, their role in that story taken over by the Ogrons. With all these Hartnell writers already on board, the production team looked to Gerry Davis - co-creator of the Cybermen - to write their colour comeback.

His first idea was to set it in a space casino. The TARDIS would arrive to find it deserted, and would come across Cybermats. 

Robert Holmes began taking over from Dicks halfway through Season 11. He wasn't keen on Davis' story and sought rewrites. These introduced the planet of gold, and space prospectors.

Holmes still wasn't happy, and the season was now developing an overarching plot, linking each story. The TARDIS would be left behind at the end of Lucarotti's totally rewritten story, and not picked up again until the end of the Cyberman story. UNIT would top and tail, and Harry would be written in then written out in these stories now that Tom Baker had been cast as the Fourth Doctor. At this point, the season was to have ended with Terror of the Zygons.

Having already rewritten The Ark in Space, Holmes then found himself having to do the same with the Cyberman story. He scrapped the space prospectors and inhabited the planet of gold with the Vogans.

The Cybermen are further undermined by being susceptible to gold. They already have a problem with radiation, and - bizarrely - with gravity. Nail varnish remover can kill them, as can quick-setting plastic. The whole point of their organ / limb replacement programme is to make them hardier, and yet their weaknesses mount. In The Wheel in Space they can space-walk, yet other writers seem to think that they can be suffocated. (Ian Marter has them breathing in his novels).

The new Cyber Leader (played by Christopher Robbie, who had previously featured as the Karkus), gives a rather emotive performance, striding around with hands on hips, sounding arrogant / pleased / angry / sarcastic. Maybe these particular Cybermen are more emotional. The script fails to make clear that they are destroying Voga for purely practical reasons - to destroy a major source of a weapon that can be used against them - so it does come across as petty revenge.

The Cyberman plan is to kill off all but three of the crew of the beacon orbiting Voga using the Cybermats to spread a toxin which mimics space plague (and turns most of its victims into mannequins). These three crewmembers will then be used to walk to the heart of Voga with powerful bombs on their backs - as the Cybermen can't go that deep into the planet themselves. Three bombs are deemed necessary to ensure complete "fragmentisation" of the planet (two to do the job plus one spare). As it is, the third crewman is killed, so it's lucky that the Doctor was there to pick up the slack.

What would have happened had a second crewman fell ill or broken his leg five minutes after arriving on Voga. The Cyberman plan goes out the airlock window.

In the end, they decide to crash the beacon into the planet. Why not just do this in the first place, without having to rely on unpredictable human factors?

When Lester detonates his booby-trapped belt buckle, why does it not trigger the main bomb? Did he know there would only be a small explosion when he did it? Why did the Cybermen risk booby-trapping the bombs for real when psychology would have done the trick?

The Cyber Leader claims there are enough parts on his ship to create a whole new army - so why not take the time to partially convert the human bomb-carriers to do what they need to do without question?

The Cyberman briefcase gizmo can track the humans only so far. The deeper they go, the less reliable. But the Doctor and company return to where the Cybermen are stationed - so why did the gizmo not pick them back up again as coming towards them?

Why did the forces which defeated the Cybermen in the war not know what happened to Voga, if its gold was so crucial to the conflict? Even if they thought that the Cybermen were never to return, all that gold would surely have been a cause for trade.

Presumably the Vogan guns use gold bullets - so why don't these have any effect on the Cybermen, considering all their varied weaknesses? Why not throw gold dust at them? The Doctor seems to think that will work.

The Doctor throws gold dust over a Cybermat and it kills it, yet later he fills another's innards with gold and it does it no harm at all. 

Why would a Cybermat have fangs strong enough to break the outer layer of a Cyberman if they are designed to kill humans? When the "space plague" broke out, why did no-one notice the bite marks on the victims' necks?

If the beacon is so essential, why has a medical team not been rushed in, in protective gear, to investigate this disease? Quarantine just stops anyone leaving - it shouldn't stop necessary personnel going in.

The transmat filters out the alien toxin, thus saving Sarah's life. Is there a setting that allows it to recognise clothes as well - or Cyberman artificial bodies? It's a great pity that the Doctor hadn't thought of this transmat trick the last time he was on the beacon - he could have saved Noah from the Wirrn infection.

This story is set around the year 3000AD. Nerva Beacon represents remarkable engineering, considering it is still in one piece 12000 years later to be used as the Ark - unless it is an extreme case of "Trigger's Broom"...

The Cybermats are redesigned - and the result is disappointing. Director Michael E Briant didn't like the classic version seen in the Troughton era, and instead approved a boring serpentine design. He didn't like these either.

The old Cyberman costumes were in a very poor state and so new suits had to be made. Being the mid-1970's, outside contractor Allister Bowtell elected to give them flares.

The story sees the final appearance of actor Kevin Stoney in the series. The man who gave us Mavic Chen and Tobias Vaughn - arguably the greatest human villains the Doctor has ever encountered - is given a horribly static mask and the role of a doddery old Vogan.

Philip Hinchcliffe was most unhappy with the Vogan masks. Despite being designed by the great John Friedlander, they appear crude and lack facial mobility. The Vogan troopers look alarmingly like Private Godfrey from Dad's Army.

We get a nice model of the Skystriker - and then they go and ruin things by cutting to stock footage of a rocket lifting off, one with "United States" clearly written on it.

You can see the ticker-tape message intended for Tom Baker hanging up just inside the TARDIS prop when he opens the doors.

What's Wrong With... Genesis of the Daleks

Doctor Who fans care a great deal about continuity - or the lack thereof. This was especially an issue of the classic era of the programme.

The biggest continuity debate centred on the UNIT dating controversy - the result of some production teams setting stories in the near future, and others ignoring this, coupled with the realities of filming in contemporary England, with its pre- and post decimal currency, vehicle registration plates, and on-screen appearances by calendars. 

The Doctor himself raised continuity issues. Was he simply a minor Time Lord who got bored and ran away with a malfunctioning TARDIS, or did he have some sort of connection with the earliest days of Gallifrey - the time of Rassilon and Omega?

Both the Daleks and the Cybermen had thrown up their particular continuity problems, thanks to their longevity and the input from diverse writers, producers and script editors.

How could Cybermen be running around London in the 1960s / '70's, if they were unknown before Mondas arrived in December 1986?

Unlike the Cybermen, the Daleks were written for by only a couple of authors - so continuity ought not to have been such a big issue with them - or so you might have thought... 

Things start to go awry with only their second appearance.

The Dalek Invasion of Earth attempted to address the issue of the creatures having been apparently destroyed on Skaro in the far future - a race of beings dependent on static electricity, incapable of moving off the metal floors of their city. How could they be ruling Earth in the mid 22nd Century? The Doctor tells Ian that this is now the middle period of their history, and the events on Skaro were at the end of their existence, millions of years in the future. What the Doctor ignores is how these earlier - therefore more primitive - Daleks could have unlimited mobility when the future - therefore more advanced - ones were tied to their metal floors.

The creation of the Daleks was said to have come about as the result of an evolutionary process. Both they and the Thals had fought a terrible war involving a neutron bomb which ended the conflict in a single day. The Thals were a warrior people, whilst the Dals were teachers and philosophers.

Radiation mutated both races. The Thals eventually became beautiful blond humanoids, but the Dal(ek)s interfered with nature and confined themselves to self-contained mobile life support units - and got stuck this way. They referred to their own ancestors not as Dals but as Daleks ("... our Dalek forefathers...").

The Daleks featured not only on TV but in their own comic strip, and this began with an origins story. The strip had Terry Nation's name attached - the man responsible for the pair of already contradictory TV stories - but we all know that they were really the work of David Whitaker, who had script edited the Dalek tele-adventures and written a novelisation of the first of them.

The strip showed the Dals as small blue-skinned people who are at war with the never seen Thals. The neutron bomb element here is that a stockpile of the weapons held by the Dals is accidentally detonated by a storm. This wipes out all the Dals save for their warlike new leader (who assassinated the older one who wanted to sue for peace) and his chief scientist, Yarveling. They come across a Dalek which they recognise as a war machine they had built before the cataclysm. Somehow it has combined with a mutant Dal to create itself, off-stage as it were. It pretty much forces the last two Dals to create more of its kind before they die of radiation sickness, getting a fancy new casing to become the first Dalek Emperor (thus proving Nation did not write any of this, as he disliked the Emperor concept).

Come 1973, Terry Nation comes up with an alternative origins story for the Radio Times 10th Anniversary Special. In this, it transpires that future humans will eventually become Daleks.

At this time, Nation had returned to Doctor Who, following the use of the Daleks to launch the 1972 season. He had agreed to write one story per season himself. 1973 saw Planet of the Daleks (very much a rerun of old 1960's elements), and 1974 then saw Death to the Daleks - which featured another military-style expedition stranded on a hostile planet (just a quarry location one instead of a studio jungle one). In 1975, wishing to use the Daleks to help set up the new Doctor after five years of Jon Pertwee, Nation was invited to submit another story and unfortunately offered more of the same. Producer Barry Letts is said to have told Nation that it was a perfectly good Dalek story - it's just that he had already sold it to them twice before. Letts instead asked Nation to come up with an origins story - initially titled "Genesis of Terror".

This is where the continuity issues come in, as the events depicted here don't quite match what we had previously seen or been told.

The ancestors of the Daleks are the Kaleds, not the Dals. They are presented as ruthless humanoids, identical in appearance to the Thals other than having dark hair instead of blond. They are also identical in terms of behaviour and temperament. The notion of a race of warriors combatting a race of philosophers is entirely absent. We also have the war lasting for a thousand years, with the nuclear weapons (such as neutron bombs) having been used up way back at the start. The only similarity to the Thal legend related in The Daleks is that the war ended with the events of a single day - the Thals destroy the Kaled dome, and immediately afterwards Davros sends in his Daleks, so both cities perish within hours of each other.

It may well be that the story told to the TARDIS crew in The Daleks was simply a folk tale, handed down from generation to generation and so corrupted over time. This explanation only goes so far. What it cannot cover is the fact that the Dalek city is surrounded by a petrified forest in The Daleks - a result of the neutron bomb - which is entirely missing from the locations seen in Genesis of the Daleks, where Skaro is a blasted wasteland. 

The Dalek city is destroyed by a missile in Genesis, and the Daleks come into being in a nearby underground bunker - so where does the city come from in The Daleks?

One issue which particularly annoys fans is the Dalek design. If these are the very first Daleks, how can they be mobile on any terrain, where supposedly future ones are limited in this area - and why do they have the vertical slats around the middle section, which only appear in later, more advanced Daleks?

One theory fans have come up with is to entirely ignore what the Doctor says about Dalek history in The Dalek Invasion of Earth. He's basically talking out of his backside. The events on Skaro were not in the far future at all, but in the ancient history of the Daleks.

After killing Davros they are sealed in by the Thal alliance of survivors. Cut off, without their creator, they simply stagnate over time and even go backwards scientifically - becoming reliant on static electricity since they never leave their city. They build their city, but prefer to remain underground due to their paranoia.

At some point, groups of Daleks do eventually leave the city and set off to explore, and these are the ones who evolve into the Daleks capable of forging empires. The ones left behind decline, and it is these which are seen to be destroyed in The Daleks.

(An alternative history features in Terrance Dicks' novelisation of The Dalek Invasion of Earth, where the Doctor simply tells Ian that there was probably more than one Dalek settlement on Skaro and they saw the end of just one of them).

(And another alternative history goes that the Doctor changes the future of the Daleks in Genesis of the Daleks, and all the events seen in the preceding stories are altered in some way - from minor deviations to never having happened at all. This is why all the stories afterwards feature Davros prominently, whereas he isn't even mentioned before this).

Going back to the cities as presented in this story - they appear to be only a few miles apart. How can these two races fight a war a thousand years long when they are almost on each other's doorsteps? And why did the conflict fail to end with the advanced weapons of the past?

Davros enters the Thal city via a secret tunnel. Why was this not used by him and the Kaleds in the past to invade the city, or to plant a bomb under it?

Once they learn of it, why do the Thals in turn not use it to attack the Kaled bunker, assuming that's where it starts?

The tunnel seems to emerge in the Thal city under a few floor tiles in a corridor. How exactly was this tunnel made, without anyone noticing this - and how did Nyder manage to get Davros through it?

Why did the Thal leadership not simply capture Davros, to prevent him developing weapons against them or to force him into helping them instead? Why trust him at all when he has just been seen to turn his back on his own race - happily condemning them to extinction for what are clearly his own selfish reasons.

The Doctor talks the Kaled government into suspending Davros' work. We don't see how he achieves this - and no wonder. It happens in double quick time. Why would they accept the word of a bizarrely dressed stranger who turns up out of nowhere with no official status?

They clearly don't like or trust Davros and his Elite but need him - so it makes no sense they would accept the Doctor's arguments against him. This involves him telling them about future events, when they don't even believe in life on other planets.

Sarah gains psychic powers - knowing that the Ark will become a beacon at some point while they're away (this was filmed after Revenge of the Cybermen, though broadcast after). She also knows all about the mission which the Time Lord gave to the Doctor, despite him never having any opportunity to tell her about it, and knows the Doctor is about to run around a corner long before he does so.

She also magically lands inside a rocket gantry after falling off the outside of it.

Why does she suddenly decide to change her clothes, in the middle of a crisis on enemy territory? And what are clearly non-Kaled Elite clothes doing in a Kaled Elite cupboard?

The Doctor knows that Nyder opens the safe in Davros' office because it is too high up the wall for the scientist to reach. Surely there are times Davros wants to access his safe without Nyder being around, so why not have one placed where he can reach it himself? What would have happened if Nyder had broken his arm, or been otherwise incapacitated? Davros would have had to give the combination to someone else, thus endangering security.

Davros shows the Elite members a big red button which he claims is a self-destruct for the Dalek nurseries. Later, it turns out that this is real. Why not just show them a fake one, with no risk involved of accidental or malicious pressing, to achieve his point?

And talking of buttons - why on Skaro would Davros have one that switched off his life support unit?

Why does the Doctor think he has set the Daleks back by a thousand years when he has only brought down a relatively short length of tunnel, and there are still a number of Daleks active within the bunker? Their creator might be dead (or is he...?) and their nursery might have been blown up, but he knows of their scientific and technical genius, which should allow them to overcome these obstacles in only a few decades at most...

What's Wrong With: The Sontaran Experiment

I always feel a bit cheated these days when watching The Ark in Space, knowing the events of this following two-part story. We have been led to believe that the people on the Ark are the last surviving members of the human race - so the stakes have never been higher as the Doctor battles to protect them from the Wirrn.

In this story, however, we discover that the Ark contains just one group of survivors - a particularly stuck-up, elitist bunch - and there are loads of other humans all over the Galaxy, getting on perfectly well without them. One is reminded of the Golgafrincham 'B' Ark from Hitchhikers Guide to the Galaxy - and maybe this is where Adams got the idea from.

We pointed out last time that the Ark is plainly seen to be in close Earth orbit - yet the Galsec astronauts fail to spot it when they come in search of their missing spaceship.

What was the missing ship doing in this part of space anyway? It is stated that Earth and its neighbourhood have long been abandoned. The ship containing the astronauts we see here shouldn't have been anywhere close by either, to have responded to the distress call.

Was there ever a missing ship? We are only told that the astronauts responded to a distress call - but this could have been faked by Styre.

Sarah sees Styre and mistakes him for Linx - yet he looks quite different to the Sontaran she met in Medieval times. The skin is paler, the features cruder, and he has extra fingers. Even the uniform is different with a darker helmet.

You meet a human who clearly knows your species - but met them thousands of years ago. Wouldn't someone on a fact-finding mission want to investigate this further?

And if Sontarans have been coming into contact with human beings since Medieval times, wouldn't they already know all the things which Styre is testing for here?

Simple common sense should tell the Sontaran High Command what happens to people if you starve or drown or crush them.

The big one. Why is Styre conducting experiments on humans on a planet on which there are no humans, haven't been any humans for a very long time, and might not see any humans for a very long time to come (he can't know about the Ark either)?

Is Sontaran High Command so hidebound by rules that an entire galactic invasion would be put on hold until a few unnecessary tests have been completed - then abandoned purely on hearsay from an alien?

Might not the Sontarans send a fleet to investigate and confirm the Doctor's claims - arriving just as all those people come down from the Ark?

All Sontarans are supposed to look the same - so why does Styre need a communications device with a TV monitor attached?

We all know that Tom Baker slipped and broke his collar bone during the filming of this story - and unfortunately it shows. We can easily spot Terry Walsh doing all the action stuff - he moves differently to Baker and the wig isn't right. All the shots of Baker are in close-up, with his coat and scarf tight around the neck to hide the sling he's wearing.

What's Wrong With... The Ark in Space

Not a lot, is the obvious answer. It's a big fan favourite, often to be found in top tens lists of greatest ever stories. There are only a couple of issues I can see.

One thing about the story which has always really annoyed me, personally, is the extra in their sleep pallet who can clearly be seen blinking as they try to watch Tom Baker and Lis Sladen play a scene in the cryo-chamber.

There's a really obvious reuse of a Sarah "horrified reaction" shot.

Space station Nerva can be seen in close orbit above the Earth. The whole point of the "Ark" was to save people from intense solar flare activity. Wouldn't the flares have affected Nerva as well, if it was so close to Earth?

The defence mechanism instantly disintegrates organic material, like the Doctor's cricket ball and Harry's shoes - yet it only fatally wounds the Wirrn Queen. There's no sign of damage on the corpse and she's able to do an awful lot before dying.

Of all the sleep pallets that Sarah could have ended up in, she just happens to be placed right next to Vira, Noah etc. in the chamber where all the action is.

And how come there was a spare pallet anyway? Surely the Ark ought to have been full?

Noah believes the Doctor and his companions to be responsible for sabotaging the station. The Doctor and Harry showed Vira the dead Wirrn Queen, lying just a few feet away from Noah's pallet - so why didn't they show it to him as well?

Producer Philip Hinchcliffe elected to cut a corridor scene between the mutating Noah and the Doctor / Vira, due to the former pleading to be killed. This has left the scene as broadcast very disjointed. The door simply closes mid-conversation, for no apparent reason, and the characters just move away.

The Wirrn life cycle. They live mostly in space, visiting planets only to breed. How exactly do they land and, more importantly, how do they launch themselves back into space if they don't use spaceships?

If they can absorb knowledge from their victims, why aren't they a technological species by now anyway? It's suggested that they've been in conflict with humans in Andromeda for a while, so must have consumed a fair few of them by now.

The Doctor never does report back to Vira about the transmat, as he gets diverted to Skaro. How long does she wait before trying to use it?

Robert Holmes' scripts were the third attempt at this story. The first, called "The Space Station" was by Christopher Langley, and the second version was by Hartnell Historical writer John Lucarotti. He gave each episode a title - "Buttercups", "Golfball", "Puffball" and "Camellias". There were aliens (the Delc) who were just heads, and others who were just bodies. The Doctor ended up hitting the head-only aliens into space with a golf club...

It's no wonder that Holmes had to do a page one rewrite.

What's Wrong With... Robot

Colour Separation Overlay works on the principle that objects of a certain colour, filmed against a backdrop of the same colour, can be keyed out and replaced with the output from another camera. Traditionally the key colour has been blue, though in more recent times green has been the favoured option. The phrase "greenscreen" has pretty much come to be the industry norm for this effect. When director Paul Bernard was coaxed away from ITV to helm a couple of Doctor Who stories in the early 1970's, Barry Letts wanted to pick his brains about the techniques which the opposition were employing. ITV favoured yellow as the key colour. As he had championed CSO at the BBC, Letts agreed that yellow should be used on Doctor Who - first appearing on Bernard's Day of the Daleks.

The main requirement of the key colour was that it did not feature too prominently in nature, and costume designers could be advised to avoid it - otherwise the bits of costume of that colour would appear invisible.

Robot required the titular creature to grow to enormous proportions in the final episode, so only CSO would manage this. Director Chris Barry was using Outside Broadcast video to record the location scenes, and this worked better with CSO. When objects recorded on video were superimposed onto film, they had a tendency to appear to float, and did not integrate properly into the composite image.

The problems with CSO should have been minimal for this story - but no-one had thought about the fact that the robot was made from aluminium. Shiny, reflective aluminium...

When the robot grows, its legs begin to vanish, along with other bits as they reflect the key colour.

(NB: the DVD and Blu-ray versions have had this problem rectified to some extent).

CSO also allowed for cheaper productions, with sets and props made model scale and simply superimposed onto the background. A real army tank would have cost money to borrow, along with limited access. Letts advised using a model - and the one they went for wasn't one constructed especially by the VFX department. They used an Action Man tank - and it looks like it. The toy lacks any sort of detail, and has tracks which don't match a real vehicle. The VFX team should have been asked to adapt it, by adding detail, but this didn't happen. Had it been filmed slowed down it might have looked better, but it is on video in real time. 

What makes this worse, is that the tank features in the Part Three cliff-hanger - so you get to see it all again the following week.

The little Sarah doll looks exactly like that - a small doll. When the robot places her on the roof, there is a CSO mismatch as she is supposed to be gripping a drainpipe - but misses by a couple of inches.

The height of the robot varies in relation to the background. No-one has thought to properly work out the scale.

Michael Kilgarriff had a terrible time in the costume. Despite lots of padding at the joints, he was badly scratched and cut. One night he had a nightmare about being trapped in a miniature submarine, and when he tried to get up the next day he found he couldn't move his legs for a few hours. There is an actual trip captured on screen, after he has broken out of Kettlewell's laboratory, and we see an almost trip as the robot descends the steps outside the SRS meeting.

On leaving the meeting, Jellicoe hides behind the robot - but UNIT troops could have easily shot him at any time. They're too busy pointlessly shooting the  robot.

The Doctor claims to have the Freedom of the City of Skaro. This must be a Thal settlement, as the Daleks would hardly be issuing such things. He also mentions that the Alpha Centauri table-tennis team use 6 bats, as they have six arms. A two armed person only uses one bat - not two - so either he's confused or they play a totally different version of the game on Alpha Centauri.

The SRS object to Sarah wearing trousers - despite these being the most practical - and rational - form of dress for both men and women. They should be objecting to impractical skirts instead.

Does skirt-wearing feminist Miss Winters know that her underlings are advocating this sexist dress code notion?

The man objecting to Sarah' dress is played by Timothy Craven - who previously played the chap who moaned about having sold his house to travel to another planet in Invasion of the Dinosaurs. They missed a trick by not having him the same character - driven to join the fascist SRS after being duped by the equally fascist Operation Golden Age.

The SRS people at the meeting are shocked to see the robot for the first time - and are then informed that UNIT are on their way to arrest them all - yet they stop to laugh at the Doctor doing silly dances and tricks. Terry Walsh's bouncer  - who the Doctor previously tripped up - is then seen simply standing back, arms folded, watching the same on stage antics, and needs prompting to try to stop the Doctor.

Much of the story revolves around the theft of components for the Disintegrator Gun. As it was developed by Think Tank, this simply draws attention to the organisation. After they get the Gun, they simply use it to open a safe, and it's the launch codes that they are really after.

Even in 1975 this bunch of scientists ought to have known what a nuclear winter might have looked like, so it is bizarre that Miss Winters insists on triggering the missiles. How many of her supporters actually made it into the bunker anyway, to create her new society?

UNIT aren't any smarter, what with them managing to lose a 9 foot tall robot in broad daylight.

Kettlewell's virus was designed to devour all metals - not just the robot's special alloy - so I hope the Doctor adapted it in some way before he released it into the atmosphere of south-east England...

When the Doctor chops a brick in two, it clearly sounds like a block of wood instead.

We see the opening section of the note which the Doctor leaves for Sarah - and when she reads it back later it isn't the same.

The BBC was undergoing one of its periodic strikes - this time involving the scenic crew. Keep an eye out for a ladder that appears in the background in a number of scenes. The crew were not allowed to touch it so they just filmed around it.

Finally, don't expect this story to represent the start of a new era, even if there's a new Doctor. It is actually the end of the old one, recorded back-to-back with Planet of the Spiders. It is a Barry Letts-produced, Terrance Dicks-written, UNIT story, so has much more in common with Season 11 than with Season 12.