When alien vampires terrorize London, it's up to a determined police inspector and an astronaut to stop them. American and British space travelers discover humanoids while exploring near Halley's Comet. The astronauts bring three of these aliens aboard their spaceship and head back to earth. However, their guests turn out to be evil vampires who kill all but one of the astronauts -- Carlsen. After the ship arrives in London, the monsters -- led by a beautiful female -- escape and wreak havoc throughout the city, transforming humans into zombies. Meanwhile, the surviving astronaut and Caine, a determined police inspector, frantically try to track down the creatures, and destroy them. But the "Space Girl" has a strange hold over Carlsen, and he has trouble fighting the urge to join her.