In this chapter, one of our heroes dies for the greater good. Read on to find out who...
After a while, the door right in front of you should open. Go through it and take the lift down. Pick up some ammo and trigger another cutscene, then go through the door, and the next door.
Walk forward and drop down again. You'll have to fight against an army of Chaos Space Marines from a distance, which means no health regeneration for you! Just be smart about using cover and you should be fine. Once they're all dead, you can go through the door.
Pick up some ammo and move forward to trigger another tough fight. This time you'll be up against hordes of Tainted Psykers, Chaos Space Marines and Renegade Militia at the same time. Be sure to make good use of the Autocannon you can find in the centre of the map. Once everyone is dead, the next checkpoint will activate.
Get rid of the Autocannon and move forward into a cutscene, where you'll finally get a ride out of there.