Grand Theft Auto IV Walkthrough

Clearing the floors leading up to your target apartment should have been easy enough, but when you reach a door with a yellow arrow in front of it, things will get slightly more difficult. Reaching that arrow will allow you to breach an apartment where three well-armed thugs are waiting for an opportunity to do you in. There's little cover for you to work with, so aggressive tactics work best here (or, a grenade, if you have any). When those initial three enemies are cleared, you can then head to the bathroom and kitchen. Both rooms are empty. But when you go to return to the entrance, you find your target in an unexpected place.

Busting out of an unexplored closet (or room), your target will run out of the apartment, leaving you on the ground with a busted nose. As he heads up towards the roof (as the game tells you), you'll have to give chase. This is one of the major reasons why clearing all of the previously-explored floors of all enemies is vital, because these enemies will show up and supplement the enemies that will already be waiting for you on your route up several flights of stairs to the roof. Cap these enemies as you did with previous foes -- you should have no issues in this chase, and there doesn't appear to be an imminence in following the target too closely.

When you arrive on the roof, the final two enemies will make themselves seen. Armed with pistols, they should be nothing for you to slay with the power of your shotgun. The red dot that represents your mark should be cowering in a corner, and you can head to his location after his friends are dispatched. He'll have his final conversation with you, talking crap to the very end. When he's slain (watch him fall to the ground!), you'll find yourself back outside of the building automatically, where you're free to take on your next mission.