The monster that challenged the world: A routine Navy experiment in California's Salton Sea produces colossal crustaceans that menace mankind. It!: In 1973, the first manned expedition to Mars is marooned. By the time a rescue mission arrives, only the leader of the expedition is left alive. He is accused of murdering his crew and is taken into custody. As the rescue ship returns to earth, the real killer, a life-devouring monster that has stowed aboard, begins attacking the crew. The remaining crew must find some way to stop it before the ship returns to a panic-striken Earth.

Container title. "Double feature." Originally produced as motion pictures: The monster that challenged the world in 1957, It! in 1958. Includes original theatrical trailer for "It."

Monster that challenged the world --(84 min.) -- It! -- (69 min.).