It! The Terror from Beyond Space

In 1973, a nuclear-powered rescue ship blasts off from Mars toward Earth with Carruthers as the sole survivor of the first mission. He is immediately suspected of murdering the other nine crew members to hoard their food and water, though he denies it, attributing the deaths to a hostile Martian life form. Commander Van Heusen orders that Carruthers be constantly watched as a precaution.

Commander Van Heusen insists Carruthers be continually accompanied by another crew member to prevent any mischief or escape. The crew remains wary, torn between relief at his survival and fear of a hidden killer among them.

During their stay on Mars, an emergency hatch is left open, allowing the alien creature to slip aboard the ship. The crew initially doubts such a creature could have boarded, but eerie noises and signs of a threat soon prove otherwise.

Kienholz investigates the strange sounds on a lower level and is killed by the intruder. His body is hidden in an air duct, delaying discovery and increasing the crew's fear.

Gino Finelli is found barely alive, but the creature attacks before help can reach him. Finelli dies, and an autopsy reveals Kienholz's body has been sucked dry of all fluids.

The crew uses hand grenades, gas grenades, bullets, and electric shocks, but the creature proves immune to all conventional methods. Fear and tension rise as it stalks the corridors.

The crew lures the creature into the reactor room, seals the door, and exposes it to the ship's nuclear pile. The creature easily breaches the shielded door and escapes back into the ship.

The creature shows extraordinary strength, tearing through metal hatches between decks. The remaining survivors retreat to the control room on the top deck to mount a final defense.

Carruthers points out the ship's higher-than-normal oxygen consumption, reasoning that the creature has larger lungs suited for the thin Martian atmosphere. This detail explains why the crew believes the creature functions differently than terrestrial life.

In a last-ditch effort, the crew suits up and Carruthers opens the command deck hull airlock to the vacuum of space. The drastic decompression creates a chance to starve the creature of oxygen.

The decompression traps the creature partway through the final hatch and it suffocates, its strength waning as the ship vents to space.

A press conference on Earth reveals the details of the rescue ship ordeal. The Earth authorities warn that Mars may be bypassed, noting the line that Mars stands for Death.