Investigating how Duds acquired the coat, Meg's father Canon Avril discovers that a member of his household staff gave it to Mrs Lucy Cash, a local loan shark, to settle a debt.

During the investigation, three people, including a young police detective, are stabbed to death in a nearby house, triggering a public outcry.

Havoc reveals that, during a confidential mission in occupied France during the war, Elginbrodde told him that the house the unit was infiltrating was his family home and that a great treasure had been located there.

The connections between himself and Elginbrodde have convinced Havoc of the existence of what he calls "the Science of Luck" and his all-consuming belief that he is destined to have the treasure has driven all his ruthless actions.

Before this can happen, however, Campion finds their hideout, forcing the gang to make a swift retreat and leave Levett behind to be rescued.

Using information provided by Havoc, Levett, Campion, Amanda and Meg agree to accompany him to Martin Elginbrodde's childhood home in France to search for the treasure.

In fact, Mrs Cash had blackmailed Avril's now-deceased wife, who was in debt to her, to help her pretend to bury her son, rather than face the public humiliation of admitting that he had been sent to prison.

Havoc and the remaining gang members follow Campion and the others to France and the now-known location of the treasure, closely pursued by Inspector Luke and the French police.