A submarine is destroyed near the
North Pole by a mysterious undersea light. The loss of this and several other ships in the Arctic alarms the world. Governments temporarily close the polar route and convene an emergency meeting at
the Pentagon. Present is
Commander Dan Wendover, the
captain of the atomic submarine
Tigershark, and
Nobel Prize-winning scientist Sir Ian Hunt. The
United States Secretary of Defense leads the meeting; he explains all that is known about the
Arctic disasters, and then describes the high-tech capabilities of
Tigershark. These include a special hull and a minisub (
Lungfish) that can be stored inside the submarine. The secretary finishes by telling Wendover that he is to take Hunt,
Tigershark, and her crew to resolve the ship sinkings, and if possible, eliminate their cause.
Lieutenant Commander Richard "Reef" Holloway,
Tigersharks
executive officer, learns that his bunkmate is to be Dr. Carl Neilson Jr., a pacifistic scientist whom he dislikes. The
Tigershark eventually discovers the cause of the disasters, an underwater
saucer-shaped craft with a sole light atop its upper dome. One of
Tigersharks scientists, Dr. Clifford Kent, briefly shows a photo of an
unidentified flying object, pointing out its similarity to this
underwater object. The submariners begin to believe that their quarry is extraterrestrial. The crew nicknames the saucer "
Cyclops" because of its single light. Commander Wendover orders the submarine's most powerful torpedoes fired. They reach the USO, but do not explode, being stopped by a gel-like extrusion coming from within the USO. The captain orders
Tigershark to ram the saucer. The submarine's bow tip breaks through its lower side and becomes trapped. Dr. Neilson pilots
Lungfish, taking Lt. Commander Holloway and a small party to board the USO. Holloway has the boarding party cut free the bow with
blow torches. Meanwhile, he explores the saucer's dark hallways after receiving telepathic messages from its sole occupant, an octopus-like creature with a single, very large eye. The alien kills all the boarding party except Holloway. The creature explains that, unlike humanity, what they create is made of living tissue. The saucer is a living creature and (as Holloway understands) is healing. The creature announces that it plans on taking Holloway and several other specimens back to its home
planet for further study. The aliens plan to modify themselves, based on what they learn about the human specimens. Once finished, they will return to colonize Earth. Holloway attacks by firing a
Very pistol into the alien's single eye, temporarily blinding it. While the eye rapidly heals, Holloway races back to
Lungfish and returns to the
Tigershark. When Dr. Neilson asks about the remainder of their boarding party, Holloway says, "Fortunes of war". The now-healed saucer sails to the North Pole to recharge its energy in preparation for leaving. Holloway tells Wendover, "Captain, if that thing ever gets back to where it came from, the Earth and everyone on it is doomed". The submariners hold an emergency meeting of
Tigersharks on-board scientists, and they develop a plan to adapt a torpedo's guidance system to convert it into a guided water-to-air missile. When the saucer rises from the ocean,
Tigershark fires the missile, destroying the USO. Holloway and the young Neilson are reconciled, with the latter conceding that his pacifism was no match for a hostile alien. ==Cast==