As Private Lance J. Lewis of the Colonial Marines, the player's objective is to escape from the military base that has been invaded by Aliens and Predators. At the start of the game, Lewis awakes in the base's brig after a cryosentence for strike offence at an officer and has no weapons, motion tracker, or security clearance. The player must find new weapons and security cards in order to fend off enemies and access new sublevels of the base, activate the base's self-destruct mechanism, and escape from the area in the escape pod. Lewis can use medical kits and food scattered in the base to recover health, but unlike the Predator, he cannot carry them and must use them immediately. Similarly, he cannot carry ammunition found on the base so the player must conserve ammo as much as possible in order to defend themselves. He can also use computer terminals in the medical laboratories to recover health, but the final amount of health possible depends on the grade of the security card which the player possesses. Lewis can also access computer terminals scattered around the sublevels to learn more about the backstory of the base after the occupation by the Aliens and computer terminals in the armory to learn more about the weapons available found on the corpses of the marines. Available weapons in this scenario include a shotgun, pulse rifle, flamethrower, and smart gun. As Lewis, the player can use both air ducts and elevators to access new sublevels. Like the Predator, Lewis can get attacked by the Facehugger and lose health by stepping on acidic blood.