Whistle Up the Devil!

ROGER GUERRIN died alone in a locked and guarded room, beyong the reach of human hands. Algy Lawrence, with sleepy eyes and a lazy grin, refused to believe in ghosts. Yet with all his detailed knowledge of sealed room trickery, he could not explain the mystery of this "miracle" murder. And then faced with a second crime which could not possibley have been committed, he began to wonder, at last, if somebody had conjured up an invisible demon who could blast out locks and walk through solid walls...
Whistle up the Devil is an ingenious brain-teaser which plays completely fair with the reader.