At a laboratory outside of a small village in the south of England, physicist Dr. Laird (Alec Mango), assisted by American scientist Gilbert Graham (Forrest Tucker), is performing a series of advanced experiments with magnetic fields -- dangerous experiments, using massive amounts of power in equipment which isn't designed to carry the load. An accident injures one of his assistants, and a request for a replacement to the Ministry of Defense brings Brigadier Cartwright (Windham Goldie) down to investigate, accompanied by a replacement for the injured man -- a woman computer expert, Michele Dupont (Gaby Andre), who helps to solve Laird's power problem, but not the larger risks inherent in his experiments. Cartwright is impressed when an interrupted experiment transforms several pieces of steel not in the test chamber into useless lumps of powder -- his report convinced the Deputy Defense Minister (Geoffrey Chater) to make Laird's project a top priority, and he sends a full security team, led by counter-espionage expert Jimmy Murray (Hugh Latimer), down to cover the laboratory. But it soon becomes clear that enemy agents are the least of the dangers manifesting themselves around Laird's project -- the hyper-magnetic fields that he has generated have been affecting the ionosphere, causing unnatural weather patterns, threatening ships at sea hundreds of miles away, and also weakening the magnetic layer that shields the surface of the earth from cosmic rays. The sudden burst of radiation from deep space causes brain damage in one man that turns him into into a homicidal maniac -- but it has also affected the insect life in the area, causing it to mutate. In the midst of this growing threat to the safety of the world, a mysterious Mr. Smith (Martin Benson) arrives in the village -- he's a well-spoken man with amazingly little knowledge of ordinary life, but a lot of awareness about magnetic fields and the work that Dr. Laird is doing. Murray is positive that he's a spy, but Gil and Michele decide that there's a lot less danger from him than from Dr. Laird, who has vowed to continue regardless of the risks. And even with Smith's warning, and Gil's and Michele's best efforts to alert the authorities and stop Laird, the forest adjacent to the town is soon swarming with gigantic beetles and other monsters.