Double Cross Purposes

The story follows an unlikely partnership between two men: the flamboyant, debt-ridden aristocrat the Hon. Vernon Lethaby, and a rugged Canadian adventurer named Joe "Digger" Henderson. Together, they head to the Highlands of Scotland to hunt for legendary Jacobite treasure (Prince Charlie's gold) supposedly buried on the Isle of Erran. Because Lethaby deeply distrusts his partner, he takes out a highly unusual policy with the Indescribable Insurance Company to protect himself from being swindled.
Enter series protagonist Miles Bredon, who is sent along by the insurance firm to ensure neither partner defrauds the company. The expedition soon takes a dark turn involving a burned body in a garage, missing keys, and an intricate web of financial skullduggery. This book stands as Knox's last contribution to the detective fiction genre, despite his long subsequent writing career. The novel is highly praised for its lyrical and witty opening chapters describing the Scottish Highland landscape.
In line with Knox's philosophy, the novel includes a physical map for readers to track the movements and clues themselves.