Lieutenant Colonel Lewis Pugh, a director of allied 'special operations' in 1943, has a big problem. German U-boats, known as 'sea wolves', are sinking Allied ships in the Indian Ocean, knowing exactly when and where to strike. Pugh's superior, Mackenzie, suspects that an enemy agent is supplying information to a German ship in the neutral Portuguese harbour of Goa. A way has to be found to destroy that spy.