Instructions
Play through the introductory level where you take pictures from a helicopter. You will eventually land on the roof of the mall.
Enter the mall through the door on the roof. Go through the hideout, then down a long corridor. A cut scene will begin, showing you a cluster of survivors barricading the entrance to the mall.
Go all the way to the back of the room with all the survivors. Another cut scene will occur and when it's over, this area will be overrun with zombies. Run up the stairs to escape the area and see another cut scene, which will put you back in the hideout.
Go to the large duct in the hideout and attempt to leave. Otis will give you a transceiver and a map of the mall. Enter the duct, then enter the door on the left side of the roof area when you come out of the duct.
Drop down to the ground floor and run straight ahead into a long hallway. Another cut scene will appear and Case 1-1 will begin.
Go through the door at the end of the hallway and Case 1-1 will end and Case 1-2 will begin. This case requires you to serve as backup for Brad. Ignore this case until the timer runs out and you will fail Case 1-2 and will receive the message that the truth has vanished, ending the Case missions.