X The Unknown - Plot

Plot

The film takes place in the Lochmouth area of Scotland, near Glasgow. A group of soldiers are taking turns using a Geiger counter to find a small and harmless hidden source of radioactivity in a wide pit area. Private Lansing finds another mysterious source of radiation where ground water starts to boil. As the other soldiers begin to run, there is an explosion. Lansing, who was closest to the explosion, dies of radiation burns while another soldier has bad radiation burns to his back. At the site of the explosion, there is a Y-shaped crack in the ground with no apparent bottom. Dr. Royston from a nearby Atomic Energy establishment at Lochmouth is called in to investigate, along with Inspector McGill who runs security at the UK Atomic Energy Commission.

That night, a local boy, on a dare from his friend, goes to a tower on the marshes. He sees a horrific off-camera sight. He refuses to tell his friend what has happened but continues running. The friend follows. Royston investigates the tower and finds an old man inside who had a canister of a formerly radioactive material now drained of radioactivity. The boy dies next day from radiation burns.

Shortly afterwards, a young doctor named Unwin is having an intimate encounter with a nurse in a radiation lab at the hospital when something off-camera reduces him to a charred corpse and leaves the nurse out of her mind and screaming.

Royston hypothesizes that a form of life, existing in distant prehistory when the Earth's surface was largely molten, had been trapped by the crust of the Earth as it cooled; every 50 years there is a tidal surge that these creatures feel, which causes them to try to reach the surface in order to find food from radioactive sources.

Two soldiers have been left to guard the pit. One goes to investigate a mysterious glow in the pit. The other one hears his screams and goes to investigate. He shoots at something off-camera, but is killed. The next day, a soldier named Elliott volunteers to be lowered into the crack, and on his way down sees a skull. Farther down, he sees the monster, still off camera, and his compatriots race to get him back to the surface again before the monster can reach him.

The army uses flamethrowers and explosives in an attempt to kill the creatures, then it seals the crack with concrete. Royston points out that the monster broke through miles of Earth to get to the surface, so a few feet of concrete would be unable to stop it. Meanwhile he continues with his pet experiment, discovering a way to neutralize radiation using radio waves tuned to a certain frequency. The monster comes out again that night; it is shown to be an amorphous glowing mass (similar to The Blob or Caltiki). Some distance away, a car with four people in it is badly burned and all four people are melted.

The thing travels to Lochmouth Atomic Energy establishment to get the cobalt used there. The Lochmouth inhabitants hide in a chapel as the monster approaches them. The creature raids the nuclear establishment before the authorities can remove the radioactive cobalt to a safe distance. As a result the creature grows even larger. As it returns through the village of Lochmouth, it narrowly misses the chapel and a little girl who has gone outside to play.

Royston and McGill hypothesize that the creature will move through the centre of Inverness, a nearby town, to reach another source of radioactive material nearby. Royston has some success with his anti-radiation device which neutralises a small container containing a radioactive source but causes it to explode violently. With no time left for further experimentation or consideration of safety, they set up two large "scanners" on lorries, and use a canister of cobalt as bait to lure the monster from where it is hidden. The idea works, but the soldier carrying the bait barely escapes with his life when his jeep becomes stuck in mud whilst leading the monster into scanner range. However, the jeep is close enough for the scanners to do their job, and the creature is neutralised and explodes a sufficient distance from the observers to avoid further injury or death.