How could two young women, in full possession of their faculties, look through a slide in a door and see a girl being murdered--and yet find the room beyond completely empty when they come to enter it with the police? This is the basis of John Russell Fearn's astonishing webwork mystery in which he reintroduces the famous backroom physicist and investigator, Dr. Hiram Carruthers. In company with the dyspeptic Chief Inspector Garth of Scotland Yard, he sets out on a tortuous trail, and though the mystery of the killer's identity is not for long in doubt, the method used is a puzzle right to the end, until the cynical master-scientist, Carruthers, fits the pieces into place. This long-lost classic of "impossible crime" is another must-have item for all discerning readers of detective fiction!