This is a very similar chase to the one from the second level of the game. Just as before, you will have to reach your destination without hitting nearby objects or losing too much health. Bear in mind that you won't have to stay close to the tracks all the time. There's a road on your right. You might as well use it. You should be able to reach the first group of enemy soldiers in just a few seconds (#1). Remember to use the G key in order to aim at the closest opponent. You should also pick-up medkits along the way (#2).
The train will enter a tunnel at some point. As a result, you will have to turn right. There's a narrow road here (#1). Once you've reached a junction, choose the path located on your right. Thanks to that, you will be able to pick up additional medkits along the way. One of the first cars will appear on the map in a few seconds (#2). You will have to concentrate all of your efforts on these gunners. Once they're gone, you will get rid of a car as well. Be careful, though. More of these thugs will arrive here shortly.
Keep firing at the gunners. You shouldn't also forget about using medkits from time to time. There's a second road on your right. You will have an opportunity to make a few jumps along the way (#1). Don't worry, you won't lose any health here. Once you've reached an open bridge, turn left. You will find yourself on a moving train (#2). Keep heading towards the locomotive.
Keep moving forward. Lara will find herself on the top of the first carriage (#1). Don't worry about that. It's part of the plan. A cut-scene will appear on the screen in just a few seconds. Get ready! You will start pressing movement keys very shortly (#2). You can't make any mistakes here. Otherwise Lara would have died. As a result, the train will come crashing to the new station. You will find yourself inside the main lab area.
There's not too much light here, so it would be best to use the flashlight all the time. Sadly, you will have to get used to it. DON'T leave this platform. Instead, use the grapple. As a result, you will be able to make a jump towards the small rope (#1), however you have to be quick about it. Otherwise it would have returned to its original position. Start swinging. You will have to reach a new ledge (#2).
There's a ladder here. You will have to use it to get to the upper floor. Now you should make a jump towards the opposite ledge (#1). Start moving towards the left edge of the screen. As you've probably suspected, you will have to reach the nearby poles. Thanks to that, you should be able to swing across to the other side of the tracks (#2). Once you're there, press the F key. You won't have to do anything else at this point of the game.
Once again you will have to use the grapple in order to pull the whole construction towards Lara (#1). After that, make a jump. Once you're on a rope, start off by climbing up a little. You should be able to avoid the fire below. Start swinging. You will have to reach an opposite platform (#2). Thankfully, it's a very easy task.
Before you decide to proceed to the next section of the map, activate the Accurate Aim mode. You will have to destroy a nearby ventilation grate (#1). Holster your weapons and make a jump towards the narrow ledge. Now you will have to climb up to the upper platform (#2). Head on to the new corridor.
Start off by running forward. Now you must get down to the lower level. You will have to avoid power cables for the first time. Thankfully, it's not too much of a problem. All you have to do is to make a single jump (#1). The game will advise you to hold the SPACE key a little while longer. I'd also recommend that. In order to avoid the second group of cables you will have to make a dive roll. There's a dead scientist here. Press the SPACE key in order to take his notes (#2). Lara will automatically start reading them.