A satellite re-enters the atmosphere and ejects a capsule, which lands approximately northwest of
Station Nord, Greenland, in the Arctic Ocean ice pack. A person approaches, guided by a homing beacon, while a second person secretly watches from nearby. Commander James Ferraday, captain of the American nuclear attack submarine USS
Tigerfish stationed at
Holy Loch,
Scotland, is ordered by Admiral Garvey to rescue the personnel of a British scientific weather station moving with the ice pack named
Drift Ice Station Zebra. This rescue is actually a cover for the real mission. British intelligence agent Jones and a
United States Marine Corps platoon join the
Tigerfish while in dock. After setting sail, a
Kaman SH-2 Seasprite helicopter delivers Captain Anders, a strict officer who takes command of the Marines, and Boris Vaslov, a
Russian defector and spy, who Jones trusts. The submarine sails beneath the thick Arctic pack ice, but is unable to break through with its
conning tower. Ferraday orders a torpedo launch to break a hole in the surface. When the inner torpedo hatch is opened, seawater rushes in, flooding the compartment and causing the submarine to nose-dive. The
Tigerfish is only saved before reaching crush depth by pumping air into the flooded area. After an investigation, Ferraday discovers that the torpedo tube was sabotaged. Ferraday suspects Vaslov, while Jones suspects Anders, continuing to refuse Ferraday's demand for more information about the mission's true objective. The
Tigerfish rises and breaks through thin ice to the surface. Ferraday, Vaslov, Jones, and the Marine platoon set out for the weather station in a blizzard. On arrival, they find the base almost burned to the ground and the scientists nearly dead from hypothermia. Jones and Vaslov question the survivors about what happened. Jones reveals to Ferraday that he is looking for an experimental British camera that used an enhanced film developed by the Americans. The Soviets stole the technology and sent it into orbit to photograph locations of American missile silos. The satellite also recorded all the Soviet missile sites. After a malfunction, it crashed near
Ice Station Zebra. When Soviet and British agents arrived to recover the film capsule, the scientists were caught in the crossfire; the only way of finding the capsule being a tracking device lost somewhere in the station. Ferraday sends his crew out to search for the capsule. Just as Jones finds the tracking device, he is knocked out by Vaslov, now revealed to be a Soviet
double agent and the saboteur. Anders confronts Vaslov and the two men fight before the dazed Jones shoots and kills the American. Vaslov feigns his innocence to Ferraday, who discovers a detonation transmitter for the capsule, which he keeps concealed. The
Tigerfish detects approaching Soviet aircraft. Ferraday lets Vaslov use the tracker to locate the ice-buried capsule. Jumping from their transport planes,
Soviet paratroopers land nearby and move in as the Americans work to free the capsule from the ice. Their commander, Colonel Ostrovsky, demands the film, threatening to detonate the capsule's explosive
booby trap should the Americans attempt to escape with it. After Ferraday hands over the empty container, a brief firefight occurs when the deception is discovered. In the confusion, Vaslov tries to take the film, but is wounded by Jones. Ferraday orders him to give the film to the Soviets. The canister is sent aloft by weather balloon for
recovery by aircraft. Moments before it is taken, Ferraday activates his own detonator, destroying the film and denying either side the locations of the other's missile silos. Ostrovsky concedes that both his and Ferraday's missions are effectively accomplished, and the standoff ends, each side beginning the return to their home countries. The
Tigerfish completes the rescue of the civilians, and sets sail back to Scotland. A
teleprinter machine report frames the incident as a successful cooperative "humanitarian mission" between the West and the Soviet Union. ==Cast==