A Fairy in the Flat: A Tommy & Tuppence Story (Tommy & Tuppence Mysteries)

Previously published in the print anthology Partners in Crime. Tommy and Tuppence Beresford are called to duty at an international detective agency. On assignment, they are told to be wary of the number sixteen. If they see it in writing or hear it in conversation with a stranger, that means they are close to finding the spy ring they seek.