First you must turn the power on and open the room that says ZC above the door by the power.

When everyone has good weapons, go up stairs by another box and one person goes outside by the window, two people go by the stairs and and when one person reloads, you shoot the zombies for them untill that person is done reloading, and one person stands in the way back by the box.

Be sure to throw granades and make a crawler don't kill the it.

Link the teleporters and upgrade a weapon. Go back to your places and reap!