The Plague Court Murders (Library of crime classics)

When Dean Halliday becomes convinced that the malevolent ghost of Louis Playge is haunting his family estate in London, he invites Ken Bates and Detective-Inspector Masters along to Plague Court to investigate. Arriving at night, they find his aunt and fiancée preparing to exorcise the spirit in a séance run by psychic Roger Darworth. While Darworth locks himself in a stone house behind Plague Court, the séance proceeds, and at the end he is found gruesomely murdered. But who, or what, could have killed him? All the windows and doors were bolted and locked, and no one could have gotten inside. The only one who can solve the crime in this bizarre and chilling tale is locked-room expert Sir Henry Merrivale. There had always been whispers of ghosts when people spoke of the deserted and sinister old mansion in Plague Court; and when Chief-Inspector Masters, genial ghost-layer of the London police, broke into the little stone house in the rear court, he found the body of Darworth, the medium, stabbed to death on the floor. The door had been bolted from within and locked from without, and there was no other means of getting in or out. Yet there lay Darworth - and besides him the dagger that had belonged to Plague Court's most evil and persistent ghost. It was a question that was not to be answered that night either by Masters, or by any of that strangely assorted group which had congregated at Plague Court. They began to ask themselves if the ghost of Louis Playge, one time assistant to the hangman, had not really come back to haunt the slime and decay of the court that bore his name.