During the first two years of the Second World War, Allied shipping losses by U-boat attacks were so high that Great Britain was in grave danger of being starved into submission. U-boats known as Milch Cows, supplying other U-boats, enabled the enemy to remain longer at sea which compounded the problem.

The situation soon became desperate. In September 1940 Commander Robert Stirling is given command of 15th Escort Group, a flotilla of Sloops based in Liverpool. His unorthodox methods of attacking and sinking U-boats, although disputed by many of his superiors, is given tacit consent by Admiral Sir Max Horton C in C Western Approaches. Stirling is ordered to take his flotilla into the South Atlantic on a secret mission.

Danger not only from the enemy but also from an unexpected source threatens to end the operation. This story is based on fact and is meticulously researched.