Saving Billy

Christina radios that she and Mason need Jack in Car 9 — Billy has lost too much blood and needs the train's infirmary in Car 6. Mason hands over a Red Keycard he says the guards dropped.

Save, drop off anything you don't need, then use the Red Keycard on the door at the far end of Car 8 to reach Car 7. Car 7 has a memo room, a guard with a drop item, and a second missile room (grab the handgun clip inside). At the end of the car, a ladder leads to a first aid kit; ignore the door to Car 6 for the moment on the way up, then head back down and through it.

Car 6 starts dark. Two soldiers guard the hallway — the second one likes to surprise you — and dropping them reveals a Pipe attachment in a nearby locker that doubles the machine gun's ammo capacity.

• Head into the glowing side room and flip the circuit breaker to restore power.
• Take the stairs at the far end up to a small lab. There's a locked door you can't open yet, but the panel beside it starts the air purifier — it takes a while, so come back later.
• Drop to the first floor, and once Christina radios that Car 6 is secured and she's bringing Billy, save your game.

Upstairs at the other end of the car, an FMV plays: Christina and Mason bring in Billy, who needs a full blood transfusion or he'll die.

Blood group B, RH+, ingredients C and D (heavy blood loss)

Once the blood is ready, bring it to Billy in the infirmary — he stabilizes, mentions trouble brewing in Car 5, and hands over a Green Keycard.

Drop back to the first floor and keep only your handgun, its ammo, and a first aid spray on you; everything else goes in the box. Use the Green Keycard on the previously-locked armory door in Car 6's hallway.

• Inside: a Plastic Explosive, a Bulletproof Vest, and, in the same locker as the vest, Night Vision Goggles. Take all three — but check the vest first: it has the initials "BM" on it.

Drop the goggles in the box for now, then continue through the armory into the VIP luggage room. An air vent in the far corner leads to a first aid kit, an ammo clip, and a ladder to the roof.