For as long as crime boss Albert Mendoza (Everett Sloane) has been running a notorious ring of hired hit men, District Attorney Martin Ferguson (Humphrey Bogart) has been hunting him down. But Ferguson cuts a deal with Mendoza's henchman Joe Rico (Ted De Corsia), and the mob boss is finally arrested. However, Rico dies mysteriously before he can testify against Mendoza.

A UFO appears above the Antarctic sea and a strange signal disrupts Earth's communications. Captain Alex Hamilton and his crew search for the origin of the signal outside the Solar System. They arrive on a planet to find the population enslaved.