When two elderly bachelors were poisoned with cyanide, a strange woman was on the scene each time

but now she has disappeared, leaving no trace. Tracking her down in a town of twenty-eight thousand people is a job to tax even Detective Inspector Bonaparte's powers.

He will need the unorthodox assistance of burglar Jimmy the Screwsman and a lightning-sketch artist, as well as all the deductive and tracking skills at his command, as he trails a killer no-one has seen...