After the cutscene, you'll be back at Nico's house. When you leave, go to the police station and talk to Moue about Marquet to find out he's been taken to the hospital. On the map you'll find the hospital below the northernmost black dot.
Enter the hospital and talk to the receptionist. When you show her Moerlin's ID card, she'll tell you that Marquet has been expecting you. Continue to talk to the receptionist until she gives you directions to Ward J2. Walk down the left hallway, and you'll see a janitor waxing the floor. Around the corner you can unplug his waxing machine, and he'll take the long way around to plug it back in. When he's on his way back from plugging the machine in, open the door next to it and grab the doctor's coat.
Head down the hallway to the left, across from the electrical plug. Once in Ward J2, talk to nurse Grendel and she'll give you the blood pressure cuff. Try walking to the door to the room where Marquet is off the screen to bottom right. A patient will stop you and ask you take his blood pressure. Return to the hospital entrance and talk with the older doctor there. He'll ask you to let his nephew Bunny follow you on your rounds, and when you get back to J2, have him take the man's blood pressure so you can get by him.
Talk with Marquet until another doctor shows up and kicks you out. Once outside you'll find that the doctor was an imposter and you'll enlist the guard's aid in bringing the door down, but not before Marquet expires. At this point you'll head back to Nico's apartment, where you can leave for the museum.
Inside the museum you'll find André Lobineau examining the cases on the far wall. Talk with him about Montfauçon, which you'll be visiting later on. After speaking with André, open the window on that wall while the guard isn't looking. When he goes to close it, you can slip into the sarcophagus at the top of the screen by the totem pole. The guard will close up the museum and you'll find that you've successfully hidden away to wait for the robbers to make their entrance.
After exiting the sarcophagus, push over the totem pole to take out Flap, and watch as Nicole in disguise drops down from the roof to knock down Guido and grab the tripod. Unfortunately you also knock yourself out in the process, and the next scene is in Nicole's apartment where you explain that you smooth-talked your way out of the police station. From her apartment, head to Montfauçon, the northeasternmost spot on the map.
Here there's a policeman sitting at a table outside the cafe and a juggler entertaining a crowd of tourists in the street. There is an entrance to the catacombs to the right of the juggler, but there is nothing to do in there. The juggler is performing right on top of a manhole cover, but you'll need to move him and get the policeman out of the area before you can open it up.
Talk with the juggler until he gives you the chance to juggle the balls. After you've tried, talk to the policeman about the clown nose, and he will give you some advice on your performance. Go back and try to juggle again, this time wearing the clown nose, to delight the crowd. The juggler will be miffed and walk off, leaving you with one of his balls. The policeman will also leave at this point since he has no performer to watch. When they're gone, use your manhole tool on the manhole to get to the sewers.
In the sewers cross the bridge and use the tool on the first arch. You'll find that it has a hollow sound and can be broken down with the manhole tool. Manipulate the mechanism you uncover, then use the wheel on the boat to release the hook and chain. Pick up the hook and attach it to the mechanism in the panel you've uncovered. Go back to the wheel and reel it in, clearing the archway in the process.
Head through the archway and take a look at the light at the top of the screen to the left of the stairway. You'll see a meeting of the Knights Templar in process and be filled in on some of the game plot. Look again when you can, and this time you'll see them wrap up their meeting and take off in the boat. Now that the coast is clear, head down the stairs. When you get to their meeting place, put the tripod on the pedestal in the center and then Peagram's gem on top of that. The light from above will be refracted into rays pointing out the letters M-A-R-I-B, spelling out your next destination, Marib, Syria.
When you get back to Nicole's apartment let her know what you've found, then head to the airport and take off for Marib.