Drift ice Station Zebra, a British
meteorological station built on an ice floe in the
Arctic Ocean, suffers a catastrophic oil fire; several of its men die, and their shelter and supplies are destroyed. The survivors take refuge in one hut with little food and heat. The (fictional) American
nuclear-powered submarine USS
Dolphin is dispatched on a rescue mission. Just before it departs, Dr. Carpenter, the narrator, is sent to accompany it. Carpenter's background is unknown, but he claims that he is an expert in dealing with
frostbite and other deep-cold medical conditions, and he carries orders from the
Chief of Naval Operations of the
United States Navy. Commander Swanson, the
Dolphin submarine captain, is suspicious of Carpenter, and calls in his superior, Admiral Garvie. Garvie refuses to allow Carpenter on board without knowing his mission. Under duress, Carpenter finally reveals that the ice station is actually a highly-equipped
listening post, keeping watch for nuclear missile launches from the
Soviet Union, a statement that convinces the commander and the admiral.
Dolphin reaches the Arctic pack ice and dives under it. It surfaces in a break in the ice and succeeds in making tenuous radio contact with Ice Station Zebra. Carpenter confides to the Captain that the commander of the station is his brother. Having obtained a bearing on the station,
Dolphin dives again, and succeeds in finding a lead from the station and breaks through a crack in the ice above. Carpenter,
Executive Officer Hansen, and two crewmen are put above on the pack ice and make the journey to the station on foot through an Arctic storm, taking with them as many supplies as they can. They reach Zebra after a near-impossible trek and find that eight of the men on the station are dead, while the 11 others are barely alive. Investigating the corpses, Carpenter finds that one of them has been shot. They find that their radio has been damaged, and so Carpenter and Hansen return to
Dolphin. The American submarine moves close to the station, and finding no open water, uses a torpedo to blast a hole in the ice. The sick men are cared for by
Dolphin. Carpenter investigates further and finds that the fire was no accident; it was a cover to hide that three of the dead men, one of whom was his brother, were murdered. He also discovers some unburned supplies hidden in the bottom of a hut, while Swanson finds a gun hidden in a petrol tank. The surviving members of Zebra are brought on board the
Dolphin, and the station is abandoned. While still under the ice, a fire breaks out in the engine room and the submarine is forced to shut down its
nuclear reactor. Thanks to Swanson's ingenuity and several hours of hard work, the crew succeeds in saving the boat. Carpenter calls a meeting of the survivors and announces that the fire was no accident. He reveals that he is an
MI6 officer, and that his real mission was to retrieve
photographic film from a
reconnaissance satellite that has photographed every missile base in the United States. The film had been ejected from the satellite so that Soviet agents operating under cover at Zebra could retrieve it; Carpenter's brother had been sent to the station to prevent this. Carpenter reveals the identity of the Soviet agents, and arrests them. The film of the American bases is recovered, but Carpenter has switched the film on the Soviets. The film they successfully sent to the Soviet surface ships is actually photographs of cartoon characters on the walls of the submarine's sick bay. ==Background and origin of plot==