Science Journalist Mark Bannerman and his photographer assistant Peter Blake meet the Professor Westfield at a London gala who is kidnapped. Blake identifies a man who was with the Professor as former U-Boat Commander Captain Kurt Swendler who vanished at the closing events of WWII. At the same time, a U-Boat is reported to have been spotted off the coast of Dover. The Royal Navy intends to track it by using the new atomic-submarine Cyana. Bannerman and Blake are invited aboard as part the restricted press coverings.