Go through New York and find the tunnels that will lead you to Georgetown. Like your last visit to the tunnels, if you get lost, follow the rats to find a way out. You shouldn't really have much of a problem however. Walk forward into the tunnels, take two lefts, a right and then a left. Follow the tunnel and it will lead you to the exit. When you hear voices, you are getting close. Meet up with your friends and then leave the tunnel.
Once outside, you need to get to the tower as quickly as possible while remaining undetected. Kill the man sitting on the edge of the well and then climb the nearby building. Make your way across the rooftops and either kill or break the line of sight of anybody you come across. Get to the roof of the building nearest the tower, kill the man on the building and then do a leap of faith into the hay in closest to the building.
A guard may investigate so kill him. Another guard will be patrolling to your left. Whistle to him and kill him. At this point, start climbing the building. You will need to be quick climbing the building for two reasons. You need to make it to the top in time but you also need to move quickly enough that you won't be noticed. You'll have to climb up and when you can't find a way up any more, start moving left. Eventually you'll climb up and circle the entire building before making it to the top. When you get there, drop down and light the fire. You have to light the fire before you run out of time to meet the constraint.
When you come down and regain control, simply start walking forward. You'll stumble into a house and come out the other side. Crawl through the wall into the fort and when you get there, it will be time for a showdown.
You can't win in a straight up fight because you've been so beat up. Instead, you need to throw your opponent into various objects to stun them and then attack to deal damage. Do this a few times to end the fight.
