Assassin's Creed 2 Walkthrough

The guy with this mission, Ugo, is standing on a rooftop in the center of the city. He asks you to free some prisoners held captive in three different locations in the city. The nearest group is just north of you. Make your way there, but beware the guards standing in the alleyways that surround the makeshift prison cells.

You can infiltrate the area by the rooftops without getting any unwanted attention. As you get near the little holding cell, a dialog between the guards triggers. Wait around and most of the guards will eventually walk away, leaving you waiting over just a single guard. You can drop down and assassinate him and then open the door of the holding cell, but expect other nearby guards to attack as you do.

Fight off the enemies and then make your way back to the rooftops with the freed prisoners in two. They're thieves so they can keep up with you as you hop around rooftops. Make your way back to Ugo, who should be just south of you. As long as you can escort at least one of the prisoners there, you can move onto the next set of captives.

The set of captives to the south are under even less strict supervision. Again, use the rooftops to get close and clear a path (by killing roof archers) that you can use on the return trip. The prisoners are at the bottom of a courtyard, with just one guard in front of their cell.

Drop down (quietly) on top of their cell, lock onto the guard, and perform a quick assassination. You should go unheard, letting you release the prisoners and take back to the rooftops for a simple jaunt back to Ugo.

We weren't able to rescue the last group, located to the west, without triggering alarms, though you can perform a double assassination on the two guards directly in front of the holding cell. Expect to have to fight off other guards that hear the event. When they're dead, escort the four prisoners back to Ugo. Do your best to avoid the water, as the prisoners will die if they fall in. And there's not much you can do about it.