The U.F.P. research vessel Thrasybulus has finished surveying an unexplored planet and prepares to head home across interstellar distances when the alarm sounds: an alien life form found on the planet and taken aboard for study has escaped from its confinement. In the confusion, several lab animals have also fled their cages, so the ship's life sign scanners cannot be used to pinpoint the location of the alien creature. The commander orders the crew to sweep every room and corridor of the ship so the alien can be recaptured as fast as possible. What the Thrasybulus crew don't know: the creature is a highly advanced predator, able to metamorphose into new forms quickly, and ready to kill without warning. A nightmarish fight for survival begins.
The Alien is a turn-based strategy game, in plot and setting inspired heavily by the classic 1979 science fiction horror film of almost the same name. The goal is to either capture or kill the alien, or, for a worst case scenario, engage the ship's self destruct sequence and escape in the shuttles. The crew consists of seven members, each one belonging to one of three character types with different skills: Officers, scientists and engineers. Officers can access the ship's armory and engage the self destruct, scientists can handle lab equipment and access the computer system, and engineers can rig equipment to construct makeshift weapons.
In each game turn, the game switches between any rooms where crew members are present. After choosing which person should act next, one from a list of pre-defined actions can be selected. These include picking up and combining items, using weapons and equipment, catching escaped animals and using ship systems like the airlock, computer or self destruct activation. After actions are taken, the crew members can be moved around the ship. To aid in plotting movements, the game displays a map of the 30 rooms of the ship that also shows crew and equipment status as well as the life scanner readings.