The spaceship "Nostromo" is enroute back to Earth after a mission of ore collecting on a planet in an other galaxy. During their flight, Mother, the Nostromo's central computer receives a distress call. The seven members of the crew, Dallas, Ripley, Lambert, Brett, Kane, Ash and Parker, five men and two women, are woken up from suspended animation to stop on the planet where the signal is intercepted.
Their mission discovers a crashed alien spacecraft and a room filled with eggs. One of them opens. When Kane approaches the egg, a creature leaps out and sticks to his face, plunging part of its body down his throat. Kane remains alive. Despite the quarantine procedure, Ash, the doctor of the crew allows the creature to enter the spaceship.
Later, the parasite facehugger dies and Kane seems to recover. Nevertheless, during a last meal before returning to suspended animation, Kane suddenly feels frightful pains in the abdomen. The Alien explodes out of Kanes abdomen, killing him and escapes to hide in the Nostromo.
So begins a hunt to capture and destroy the monster. But the hunter and prey soon become entwined in a hunter-hunted exchange The creature rapidly grows in size and is revealed to have highly acidic blood, rendering it more difficult for eliminate without causing serious damages to the hull of the spacecraft. The creatures intelligence allows it to not only escape its pursuers but to trap them and kill them one at a time
By questioning the Nostromo computer, Ripley discovers that the distress call was not a S.O.S. but rather a warning. Ripley begins to suspect Ash to preserve the alien. Her suspicions become true when the former atempts to kill her. Finally, Ripley will have reason of Ash who in reality is a android elected by the company to return the Alien on Earth, this one representing a powerful weapon.
The only survivor, Ripley decides to leave the Nostromo...
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She programs the ship for auto-destruction, then embarks in a small rescue vessel with the cat Jones, the mascot of the crew. What she does not see, is that the Alien has equally embarked in the shuttle. Ripley, will succeed to get rid of the monster by ejecting it out in space...
Correction : the turk