X The Unknown 1956

X the Unknown is a 1956 British science fiction horror film directed by Leslie Norman and starring Dean Jagger and Edward Chapman. It was made by the Hammer Film Productions company and written by Jimmy Sangster. The film is significant in that "it firmly established Hammer's transition from B-movie thrillers to out-and-out horror/science fiction" and, with The Quatermass Xperiment (1955) and Quatermass 2 (1957), completes "an important trilogy containing relevant allegorical threads revealing Cold War anxieties and a diminishing national identity resulting from Britain's decrease in status as a world power".
The film opens in rural Scotland. In a deserted field, soldiers take turns familiarizing themselves with how to use a Geiger counter. Suddenly, there is an explosion. One soldier dies of radiation exposure while another is badly burned. At the site, there is a Y-shaped crack in the ground with no apparent bottom. Dr. Royston of the Atomic Energy Laboratory, is called in to investigate. He's later joined by "Mac" McGill, who runs security at the UK Atomic Energy Commission. That night, a local boy witnesses an horrific off-camera sight. He dies the next day of radiation burns. Royston investigates and comes upon a tower occupied by an old man in possession of a canister left over from previous radiation experiments. Later, in a local hospital, a young doctor collapses and melts after witnessing the same off-screen horror as the boy.
The same evening, when two soldiers mysteriously die while guarding the Y-shaped crack, Royston's colleague Peter Elliott volunteers to be lowered into the pit to investigate. Before long, he encounters the same off-screen horror as witnessed before. However, he is pulled out of the pit in the nick of time. The army uses flamethrowers to try to kill the unseen creature but to no avail. Royston hypothesizes an explanation for the phenomenon. His theory involves a form of life that existed in distant prehistory when the Earth's surface was largely molten. This entity had been trapped by the crust of the Earth as it cooled. But every 50 years there is a tidal surge that these creatures feel, causing them to reach the surface and find "food" in the form of radioactive sources.
The thing is finally revealed – an ever-growing blob, now crawling its way toward the Laboratory to feed on cobalt being used there. Royston and McGill accurately predict its movement. They proceed to a location where they set up two large "scanners" on lorries and a canister of cobalt as bait. Peter drives the bait by jeep, drawing the blob's deadly attention. Eventually, the creature is neutralized and explodes. But as the team approaches the crack from which the monster had emerged, a second, more powerful explosion occurs, knocking several off their feet. Puzzled, the team continues approaching the crack, presumably to make further tests, as the film comes to an end.