A spa-goer resorts to murder.

Even down in New Zealand, war-fueled spy fever is running wild. Near the decaying sulphur springs of Colonel and Mrs. Claire, the strange lights and signals being sent to foreign ships at sea mean there's a spy in their midst. Soon an even darker sign appears--a health-seeker with untoward intentions meets his demise in the mud baths. And when a new arrival appears, one who possesses the cunning of a criminal and the insight of a psychologist, can Scotland Yard's Inspector Roderick Alleyn be far behind?