It is May 1944, two weeks before D-day. Britain stands poised for the long-awaited invasion of France - thousands of troops wait anxiously for the orders to come for embarkation. MI5 is horrified to discover the top-secret codewords for the invasion suddenly appearing as clues in the Daily Telegraph crossword. Two agents are immediately dispatched to confront the culprit, the headmaster of a boys' school in southern England.