A test pilot named John Corcoran returns from a pioneering near-space flight, completely intact physically (save for a small gash on the forearm) but unresponsive and apparently dead.
A team from a NASA-like base housed in an old radio station recovers his body and then the facility loses electrical power and communication with the outside world. The pilot recovers and returns to normal ambulatory functioning, but with strange new blood cells and, it seems, prawn-like embryos in his abdomen. Soon, the body of Dr. Wyman, the lead physician, is discovered suspended upside-down in the exam room - headless - assailant unknown; the adult alien makes a brief appearance at the base and then flees, and Johnny pleads with his colleagues for understanding of this new life form, whose intentions he somehow seems to sense.
Despite Wyman's death, Corcoran does not believe the creature is evil, but rather simply misunderstood. He implores the others to give the creature a chance to explain its actions, and asks that they not condemn it as a monster simply because it is different. As the others plot to destroy the creature with improvised gas bombs and flares, Corcoran flees the station and finds the creature in a nearby cave. After consuming Wyman's brain, the creature is now able to speak with the scientist's voice and has absorbed his knowledge. Corcoran asks whether Wyman's death was needed, but the creature insists it was a necessary sacrifice.
The others arrive to destroy the creature, but hesitate because Corcoran will not step aside and let them throw their bombs. The creature insists it is not an evil monster, but an intelligent alien who has come to Earth to save the human race from its own self-destructive tendencies. It explains that Corcoran's body has been implanted with its embryos, which will allow the alien species to multiply and take over the human race, which the creature claims is the only way to truly save humanity.
Upon realizing the creature is forcing the will of its species on the human race, Corcoran concludes the creature is evil after all and commits suicide so its embryos cannot come to fruition. The others then throw their explosives and kill the creature, which in its dying breaths warns that others from his species are waiting in space and will return one day to conquer humanity.
- Michael Emmet as Major John Corcoran
- Ed Nelson as Dave Randall
- Angela Greene as Dr. Julie Benson
- John Baer as Steve Dunlap
- Tyler McVey as Dr. Alex Wyman
- Georgianna Carter as Donna Bixby
- Ross Sturlin as The Blood Beast
- This was released in one of American International's pre-packaged double features. It was paired with Roger Corman's She Gods of Shark Reef (1958), which had gone unreleased for a year and a half.
- The music is from a stock score which Corman would also use in Attack of the Giant Leeches, which was also directed by Bernard L. Kowalski.
- The Blood Beast costume was also used (and worn by the same actor, Ross Sturlin) in Teenage Cave Man.
- Shot in 7 days.