Walkthrough: You'll begin this mission on board of a new carriage, however you'll only be allowed to look around. Get ready, because you're about to take part in a new vision. You can choose here between moving towards an alien creature #1 and moving towards one of your allies #2. Make sure to read the chapter named Endings (it's spoiler-free) to find out how this choice can affect the final scene of the game.
Wait for the carriage to stop #1, because this is the moment when you'll regain full control over the main character. I wouldn't recommend waiting - instead approach a stationary flamethrower right away #2. Notice a temperature indicator in the lower left corner - you won't be allowed to overheat the flamethrower, because it would then need a few seconds to cool down.
Wait for monsters to start showing up in the area. You should be aiming at the train tracks located directly in front of you #1, because this is where most of the mutants will land (even if they were performing a lot of jumps earlier on). Sadly, even if you're careful, some of the monsters will grab onto the carriage #2. Make sure to eliminate them as soon as possible. Naturally you'll have to prevent too many of them from getting through, because they would eventually kill you.
Keep defending yourself until your allies have fixed the carriage. You'll now watch a cut-scene featuring a well-known anomaly #1 and you'll soon leave the carriage. Proceed towards the nearest passageway #2 where this mission will come to an end.