July 2008. Prometheus 4, the first of a new generation of super-tankers, plunges round the North Cape, heading for its rendezvous in the Barents Sea with Titan 10, from which it will collect its cargo. Formerly a nuclear submarine, Titan 10's missiles have been replaced by tanks carrying 10,000 tons of oil. Oil collected from a wellhead deep beneath the Kara Sea. When the two vessels meet, there is no response from Titan 10 and Captain Richard Mariner crosses to investigate. The submarine is utterly deserted. And the oil is gone. Mariner and his crew follow Titan 10's computer guidance records back along the track of her last, mysterious voyage into the ice-bound, storm-wracked Kara Sea - to face the greatest dangers of all.