In 1995 Czech scientist Jan Benes escapes from behind the Iron Curtain and is brought to the United States for interrogation. U. S. scientists are able to reduce objects, including people, to the size of bacteria, but the miniaturization can be sustained for only 60 minutes. The Czech scientist has learned the secret of prolonging the miniaturization; but before he reveals this knowledge, he sustains a severe brain injury which can be treated only from within his body. A plan is conceived whereby a crew of five will be placed in an atomic-powered submarine, miniaturized, injected into the scientist's bloodstream, and set on a course through the arteries to the brain. In addition to American secret agent Grant, the crew consists of Dr. Duval, the surgeon who will perform the operation; Cora Peterson, his assistant; Dr. Michaels, a circulatory expert; and Captain Owens, the sub's pilot. To save some of the 60 minutes, the group decides to stop the scientist's heart to allow the submarine to pass through the heart. Then Grant and the crew leave the sub, and by means of a snorkel tube attached to the patient's lungs, replenish their oxygen supply. As they near their destination, a nurse in the operating room drops a pair of surgical scissors, and the sound causes tremendous vibrations in the sub that hurl the crew from their positions. With only 6 minutes left, Dr. Michaels reveals himself to be an enemy agent intent on sabotaging the mission. The remaining crew members escape as white corpuscles envelop and digest both the submarine and Michaels. The operation is successfully performed by removing a blood clot with a laser beam, and the four survivors leave the scientist's body by swimming along the optic nerve and emerging through a tear duct.