Henry Ireland, a failed landowner, dies unexpectedly in a riding accident, leaving a highly strung young widow. Not far away lives Ireland's friend James Dixey, a celebrated naturalist who collects strange trophies—a stuffed bear, a pet mouse, and a wolf that he keeps caged in the grounds of his decaying house, lost in the fog on the edge of the fens. The poachers, Dewar and Dunbar, with their cargo of pilfered eggs; Esther the observant kitchen maid, pining to be reunited with her vanished admirer; the ancient lawyer Mr. Crabbe, made careless by snobbery; John Carstairs, in search of his cousin, the elusive widow; an enigmatic debt-collector, busily plotting an audacious robbery; various lowlife henchmen; a beady-eyed country curate who sees more than he should; and Captain McTurk of Scotland Yard, patiently investigating the circumstances of Mr. Ireland's death and many other things besides—all are drawn into a net of intrigue with wide and sinister implications.