A fishing vessel sets out and contact is lost. A search ensues, nothing is found and is called off. A relative of the crew thinks the search should go on and starts to organize an expedition to find the ship causing disquiet in London.
The inquiry into the sinking begins and allegations of Russian intervention are made. The momentum for an expedition is lost with its organizer compromised. Flotsam is found and sent for examination and while a letter attracts attention.
There is a death in suspicious circumstances, the inquiry hears allegations of spying. The journalist begins to think the ship was spying. He has a photograph that might prove it. London gets more worried about his activities.
The journalist and his girlfriend survive an attempt on their lives and go on the run from the renegade London operative. The journalist goes into hiding, his girlfriend investigates the NATO exercise taking place when the Caistor vanished.
The girlfriend gets the first major clue of what happened to Caistor that night and the journalist skips his hiding place and heads to Norway. Meanwhile the renegade London agent is pursuing the journalist abroad.
The journalist and the renegade London agent finally meet each other in Norway. Finally the full story of what happened to the Caistor that night is revealed.
