During World War II, German submarines are sinking thousands of tons of British merchant shipping. British intelligence, based in India, believes that information is being passed to the U-Boats by a radio transmitter hidden on board one of three German merchant ships interned in Goa, then a colony of Portugal. Since Portugal is neutral, the ships cannot be attacked by conventional forces.
The head of the Indian section of the Special Operations Executive (SOE) authorises attempts to kidnap and interrogate two known German agents, but these operations both fail. An approach is then made to a Territorial unit of British expatriates, the Calcutta Light Horse, to carry out the mission on its behalf. They all volunteer – all are trained in military skills and keen to ‘do their bit’.
Whilst the volunteers are trained, Stewart and Cartwright travel covertly to Goa. By a mixture of blackmail and bribery, they arrange diversions on the night of the raid. A party is to be held in the Governor’s palace, a brothel will offer free entry to sailors from ships in the port and a Carnival with fireworks will be held. Stewart has a brief affair with Mrs. Cromwell, a mysterious and socially well-connected woman, who turns out to be a German agent and the main conduit to the German ‘Master Spy’, known to the Germans and the British by the code-name Trompeta (Trumpet). She is eventually killed by Stewart, after she attempts to kill him but not before she’s killed Jack Cartwright.
The raiding party sail around the coast in a decrepit and barely seaworthy barge; they set mines on the hull of the German ships in Goa. They then board one which is being used to transmit signals to u-boats, catching the depleted crew off-guard. Despite Pugh’s order that there be no shooting, several German sailors are killed. The ship is set alight and the party withdraws, watching as the ships sinks. The final scene show a surfacing German u-boat which is expecting to hear a signal from the now sunken ship.