Returning home late one night, bachelor Herbert Wrayson discovers a young woman searching his flat. After interrogating her it becomes apparent that she thought she was in the flat of his upstairs neighbour, Morris Barnes. Wrayson soon finds himself caught up in a murder mystery, all the while falling for the lovely young woman. But who is she, what did she want with Barnes? And does she have anything to hide? A classic whodunnit from the skilful mystery author E. Phillips Oppenheim.