A ship has been entombed in ice, but what originally appears to be a natural result of a fire in the frigid north Atlantic soon is identified as murder and cover-up. Major Dirk Pitt is assigned by Admiral Sandecker to investigate and search for a missing undersea probe invented by the now deceased Kristjan Fyrie. Pitt and scientist Bill Hunnewell locate the ship in the iceberg and investigate but discover more questions than answers.

As Pitt and Hunnewell attempt to fly to Iceland to continue the investigation, their helicopter engages in an air battle with a mysterious black jet. Pitt causes the black jet to crash, but the helicopter crashes as well and Hunnewell is killed. Pitt continues to encounter attempts on his life, and when Sandecker and his assistant Tidi Royal join him in Reykjavik, they, too, are in danger. Pitt meets Kirsti Fyrie, Kristjan's twin sister, and her fiancé, Oskar Rondheim. Pitt meets Jerome P. Lillie, who is an NIA agent for the USA. Lillie reveals to Pitt that the NIA and the NUMA have discovered that Hermit Ltd has ties to Rondheim and Fyrie, and they believe they are all joining forces for some reason. Pitt soon realizes Rondheim is the man behind all these attempts to kill him, and that Rondheim controls the probe and Kirsti. Pitt assumes the role of a homosexual artist to fool Oskar into thinking Pitt is harmless. Pitt and Sandecker find the black jet on the bottom of the north Atlantic and are again targets for death, but escape.

Pitt and Tidi are invited to the Fyrie mansion, where Oskar and James Kelly reveal their plans to take over the world, starting with Central and South America, and using the undersea probe to locate immense riches to fund their scheme. Pitt, Tidi and thirty others are kidnapped, drugged, and left in a ravine in Iceland to die, thus providing a distraction for the media while Hermit Ltd. enacts its plan. Even though Pitt has been beaten by Rondheim until almost dead, he is able to go for help and brings it back in the form of an old Tri-Motor airplane. Once everyone is safe, Pitt allows himself to be treated for his injuries. Soon, however, he is enlisted by the director of NIA to continue and complete the investigation of Hermit Ltd. Pitt is taken to Disneyland in California, where he, Kippman and Lazard finally defeat Rondheim and arrest Kelly.

At the end, Pitt tells Kirsti that it is all over; her controller Rondheim and Kelly are under arrest, and Pitt is aware that Kirsti is actually Kristjan with a sex change operation. Pitt has arranged for Kirsti to be set free, on the condition she will work with NUMA on refining the undersea probe to be used for good, not evil. To punish Kirsti for changing her personality from the kind, giving Kristjan to a selfish beautiful woman, Pitt rejects her offer of sex, and walks away.