Tim Hanley, an American agent, posing as a lawyer with the United States Embassy in London, and Reggie Oliver, a Scotland Yard detective, posing as a music critic are both keeping their eye on Carla Nillson, a famous singer, whom they suspect of espionage. They all meet in London, then in Lisbon, and eventually in New York City, where Carla sings on the radio.

A spaceship is sent to Mars after an alien distress signal is picked up. They find one survivor, but when a crew member is found drained of blood it's evident they have rescued a bloodsucking monster. Uses footage from Encounter in Space (1963).