Trent is a man with no memory of his life before the past ten days. His left hand has been replaced by an advanced computer shaped like his missing hand and protected by some transparent material. Three fingers are missing; the computer tells him they must be reattached before it can tell Trent what is going on. Trent is being hunted by a handful of humanoid aliens called the Kyben; they have the missing appendages. The action takes place in a large rundown office building which the Kyben have sealed off from the world. In this deadly game of hide-and-seek, Trent enlists the help of Consuelo Biros (actress Arlene Martel,) a woman who works in the building.