Alien Trilogy is based on the first three movies of the Alien film series. The game actually opens with the beginning of the second in the series, Aliens. You play the part of the space marine Lt. Ellen Ripley. Communications with the colonists of LV426 have been lost and you have been sent to the colony to determine what the problem is. Soon after landing it becomes apparent that the communications problem is the result of an alien attack.
Your task is to fight your way through 30-plus levels filled with hostile enemies. Destroy aliens, Alien Queens, and other marines who are trapped inside the alien walls. A large arsenal of weapons is at Ripley's disposal. There is everything from shotguns and flame-throwers to pulse rifles and smart rifles. Extra ammunition and first aid boxes are lying around the levels for you to help yourself to.