On a distant planet called Sirius 6B in the far future, a war has broken out between a mining company called New Economic Bloc (NEB) and the workers who call themselves the Alliance. The Alliance have created a machine called a screamer that looks like a little clawed robot rodent with buzzsaws to kill the NEB soldiers.
Screamers hunt by detecting people’s heartbeats. Alliance use a device to block their heartbeats. The war has gone on far too long and the planet is a wasteland. The Alliance led by Hendricksson (Peter Weller) get a message from a dead NEB solider saying that the NEB wants to discuss a truce.
Hendricksson’s superiors claim that a truce is unnecessary because they are working on one on Earth. Hendricksson figures that means that both sides have abandoned them on Sirius 6B and decides to go the meeting.
On the way they run into a young boy holding a teddy bear. At night they get attacked by a screamer that looks like a lizard and their blockers didn’t work. When they reach the NEB headquarters they find that only two soldiers, Becker (Roy Dupuis) and Ross (Charles Powell) and a black marketeer named Jessica (Jennifer Rubin) have survived.
The screamers have evolved and they are looking like humans like the boy that Hendricksson found. They race back to Alliance base on to find that everyone has been wiped out too from the new human screamers.
Now it becomes a game of who is human and who is a screamer.
Based off of a Philip K. Dick story called Second Variety, an early draft of the script was written by Dan O’Bannon.