If you're an Innocent crew member...
Your ship has been infiltrated. Two of your crew mates have been replaced with shape-shifting Aliens.
Scavenge weapons and tools from around the ship and use any and all of your sleuthing methods to identify and kill the Aliens before they kill you.
If you're a
You look, talk, and walk like a crew member, but deep down inside, you are a bloodthirsty Alien.
Work with your Alien partner to gather evolution points from unsuspecting innocents.
Have enough? Transform into your true form and wreak havoc.