A hardened mechanic (Bruce Willis) is one of a few chosen to stay awake and maintain an interstellar arc fleeing a dying planet Earth with a few thousand lucky souls on board... the last of humanity. Unfortunately, humans are not the only guests on board. A shapeshifting alien creature has also taken residence and its only goal is to kill as many people as possible. Now, the crew must think quickly and try to stop this menace before it destroys humanity.