Once you regain control, you'll run into the man group of Marlowe's men in a large courtyard area. You can do this stealthily, but I don't see much of an advantage to it. If you do it quietly, fewer people will spawn, but you'll have to do all the takedowns yourself. If you get into a firefight, your whole gain will join in and make it fairly easy. Plus, the firefight is just a sniper's dual in which you have access to lots of assault rifles and pistols that are lying on the different stone tablets. Just pick out a target, then settle in and take out the reinforcements.
Once again, cross the path and look for a gate and some stairs that will take you up to a large tower structure. Go up the steps with your group, and reach the second floor. There are a lot of thugs up here, including a new armored mercenary with a shotgun. The halls are narrow, so either use a shotgun or fire from the hip for easy kills. Running forward and using melee is a good idea too. The men are usually spread out enough for easy kills. The armored merc will show up last, so just rush him and take him out with a longer series of attacks. There's also another treasure up here. Check all the windows to find it.
When you're ready to do so, go up the steps. Leap over the rock that falls until you get trapped in an ambush. After it finishes, you'll be left outside with some chains. This is actually a simple puzzle. You can run along the walls with your chains, and climb up too. Use a mix of both to climb up the chains to make your way back up to the top of the tower. You will come under fire, but each of the chains have a large stone block above them that provides fairly good cover. Just use your pistol to carefully pick the unlucky mercs off.
Once you're at the window, you can pop back in and find a few more guards. Just turn to your right and fire away at the group of three. At close range and without much cover, this should be easy. Look around and you should be able to spot another pair of guards across from you. Take cover and pick them off as usual.
There's a single door that leads to the staircase, so go ahead and open it up. Unfortunately, this will let a brute out. I expect that you know how to deal with them by now though. When he's down, go up to the top of the tower with your group.
You'll get a short break for now, so enjoy it. Just look for the cup of the big dipper and then go to the right and focus on the littler dipper's tail. This will start up an unfortunate exchange though. For now, just run forward with your group until you get to the tower at the end. There should be a stockpile of sniper rifles here, so grab one, then get ready for a challenge.