Talbot and Katherine Marlowe enter their black car, ramming Charlie Cutter on their way. Once the car had left, Nathan Drake and Victor Sullivan get up, revealing that Cutter's shooting them was just an elaborate ruse. Nathan complains to Cutter about the rough handling he received, Cutter states that Nate had told him to make the fight look convincing. They hear sirens, and realize that they have to get out of the area, before the police come. The three make their way across London, climbing over various structures and vehicles to reach their destination. Once done, they stop on the street, where they are joined by Chloe Frazer, who leads them to her van and hands out each a flashlight and a silenced pistol. They decide to track down where the hidden library was located, first by getting into the building that Marlowe's van disappeared into. Nathan climbs up the drainpipe to the roof, then gets in the window and lets in the others. However, Marlowe's car has vanished. Some investigation leads to Nathan discovering a well-hidden door that leads to an extensive array of tunnels, which they are able to navigate thanks to Nate's exceptional climbing skills. They also encounter several armed agents, but are able to subdue them easily enough. Eventually, they reach a vast underground library, which serves as Marlowe's headquarters.
I. Run towards Sully and Cutter and squeeze through the tight gap, collecting Treasure #13 when you reach the other side. Vault the low fence, then climb to the drainpipe beside the locked gate; when Cutter presents his alternative solution, drop to the ground with O. Clamber over the next barrier, approach the yellow trailer and tap O when prompted, then use L to move it into position.
II. When you reach the green shutter door, climb the nearby drainpipe and follow the route upwards. When the upper section of the pipe breaks away, use X and L to jump to safety. Drop onto the roof at the end of the climb, then jump onto the pipe below the satellite dish. Swing over to the sign, vault to the other side, jump to the metal pulley behind Nate, then clamber through the window to the left.
III. Nate won't survive a drop to the floor below, so you'll need to take a relatively circuitous route to ground level. Move to the other end of the wooden walkway, then jump over to the pipes on the wall; from here, move over and drop down to the open window. After a detour for Treasure #14, change sides on the wall by passing through the open window, then use the pipe and ledges to reach the ground. You can now collect Treasure #15. Approach the shutter door and press triangle to open it.
IV. After Sully, Cutter and Chloe enter, there is a small puzzle to solve: where is Marlowe's car? Nate's companions will make comments to draw him to positions where the clues lie. In the first, Cutter will call him over to look at recent tire tracks. After this, look for four nearby stones on the ground with wet tire marks. Stand on one of these, and Nate will discover that they are pressure pads. Move to another stone, and a cutscene will ensue. Press X to jump at Nate's prompt. Finally, follow the onscreen instructions to hold up on the D pad and use R to shine your flashlight at the closest wall - unlocking the hidden light sensors will open the way.
V. Follow the tunnel until you reach an apparent dead end, examine the nearby door with triangle, then draw Nate's pistol to shoot the lock. Use L to squeeze through the gap. When you encounter the two besuited henchmen, shoot the opponent on the right first; Cutter should take care of his companion, though you can deal with both if you're quick.
VI. Two further assailants enter the room via an opening above a ladder. Once they have been neutralized, collect Treasure #16, climb the ladder and drop into the waterlogged room just beyond it. Though you may notice that your opponents drop the .45 Defender pistol, you cannot collect these: Sully and Cutter insist that Nate should stick with his silenced sidearm.
VII. You must use the pipework in the shaft to safely reach the area below, but be sure to collect Treasure 17 and the Special Treasure before you begin the descend. Jump back to the long vertical pipe after collecting Treasure #17, then hold L down to slide rapidly to the bottom. In the next room, take cover behind the wooden pallet on the left as the two henchmen approach. Wait for the prompt from your companions and then emerge from cover to fire. Should you delay too long, Sully will deliver a stinging rebuke.
VIII. In the next room, use the pipes on the wall to reach a ladder. Once Nate kicks it down, climb into the chamber above. Collect Treasure #18, then follow the route to reach a lever. Sully will asks Nate to give him a boost to reach a ladder leading to the opposite lever, but there's no need to do this: if you ignore him, Cutter will step in to assist. Press triangle when you reach the lever (and then tap the button rapidly when prompted) to lower a platform. Run over the walkway, then drop over the edge through the opening to your left on the other side. Follow the tunnel to reach the next chapter.