In his tenth and final adventure, set just after the end of the Second World War, Lemmy Caution is in Paris investigating the theft of secret State Department documents. In the opinion of his chief, however, Lemmy has fallen down on the assignment given to him - to trail two suspected enemy agents, one a Frenchwoman and one an American - and he is ordered to bring them in. The trail leads from Paris to England, and a thrilling conclusion in the Surrey countryside.