A young woman’s body is hauled out of the English Channel by a passing yacht, and it matches the description of a woman named Thurza Darke given in a circular fromInspector Frenchof Scotland Yard. Just the day before he’d been sitting alongside Thurza, listening to her story about the “suicide” of her friend. Thurza had been ensnared in a scam perpetrated by a man with a purple sickle-shaped birthmark on...