You’re back in Mars City with an objective to report back to Sgt. Kelly. There will be a z-sec hiding behind the big crate on your right, head up the small stairs on your left and a ladder will be lowered for you. At the top an engineer will chat to you and you can turn left and crouch to enter the vent. Make sure you’re flashlight is on and collect the armor in the vent and then follow it round. When you drop down two zombies will spawn in one behind you and one in front. Take them out and grab Marcus Stanton’s PDA from the desk before taking the door on the left, shoot the body lying by the door before you go through. There’ll be a z-sec to kill in the corridor beyond, turn right and through the door, there’ll be another z-sec and then you’ll see through the glass there’s an imp eating someone, don’t worry he can’t get to you. Pick up the card on the desk on your left and go back out and use it to open the other door.