The Xenos just keep coming. You've got to hold them off until all have been destroyed before you can get out of here. That's where you find yourself in Nice Guys Finish Last, a new Zombicide: Invader scenario that CMON has posted online.
From the post:
Hold them off! In this special scenario, Survivors may only escape after the Xeno Deck has run out of cards. And you have to protect the crew members while at it! Good guys finish last? Not on our watch!
This scenario for Zombicide: Invader is meant for only 4 players! Pick your crewmates wisely and click here to download the scenario.