Seven space cowboys must defend a planet from evil invaders who are terrorizing the innocent people in a faraway land. They citizens hire the warriors to fight Sador (John Saxon) who is cruel and despotic. Gelt (Robert Vaughn) and Shad (Richard Thomas) join Cowboy (George Peppard) as the mercenaries who agree to defend the planet. Dr. Hephaestus (Sam Jaffe) has enough technical knowledge to give the hired guns some assistance in their cosmic battle set for one week later. In fact, Saint-Exmin (Sybil Danning), a woman, joins the crew to prove she is as good as a man at fighting, but lovely Lux (Marta Kristen) only has eyes for Cowboy.