A mysterious killer strikes in a city where crime should be impossible. For generations, police investigations have been unnecessary in the city of Basle. Tiny tracers identify any criminal as soon as an illegal action takes place, and this has made the city virtually crime-free. But now the city is torn apart by a series of gruesome murders committed by a shadowy figure known only as the Baron of the Mists. And qualified witch and detective Roberta Morgenstern and her young associate Clément Martineau are on the killer's trail. High-speed chases across rooftops and through the city's winding streets lead Roberta and Clément to the Queen of the Gypsies, the pirates of the lagoon, the practicers of some very dark alchemy, and finally to the deadly Baron of the Mists himself. . .