- By John Dickson Carr, as Carter Dickson
- First published: US, Morrow, 1934; UK, Heinemann, 1935

This 1934 novel, which introduced Sir Henry Merrivale, is one of the best Merrivales. Although somewhat over-written, Carr recognises the effectiveness of understatement in conveying the haunted house and its malevolent ghost, supported by the Plague-Journal, a document which M.R. James Himself would have been proud to have written. The murder of the fraudulent psychic and murderer, stabbed to death in a locked room, is one of Carr’s most ingeniously worked-out crimes, and is as equally ingeniously unravelled by the Mycroftian Sir Henry Merrivale, who does a brilliant job of deducing which of the gargoyles committed the murder and how. It is certain that no reader will ever get the murderer’s identity, very cleverly hidden from the reader; yet the clues are all there, as they are to the method, which, like the identity of the murderer, is thoroughly unexpected.
Blurb (US)

There had always been whispers of ghosts when people spoke of the deserted and sinister old mansion in Plague Court, and when 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 without, and there was no other means of getting in or out. Yet there lay Darworth – and beside him the dagger that had belonged to the one-time hangman’s assistant – the ghost of Louis Playge.
“Ghosts?” growled Masters, raising his eyebrows. “Looks like it. But there are no such things. Now, how the devil…”
The question was not answered that night, either by Masters or by any of the strange group assembled at Plague Court. Old Lady Anne, imperious and domineering, clutching at the insidious atmosphere of the old house, hoped for some sign from the beloved dead. But the rest were combatting the atmosphere: bluff, prosaic Major Featherstone, who feared nothing but Lady Anne; Marion, young and lovely, engaged to young Halliday; and Ted, her neurotic young brother who was fascinated and terrified at once. Nevertheless, they began to ask themselves if the ghost of Louis Playge had not really come back to haunt the slime and decay of the court that bore his name.
Contemporary reviews
New Statesman (Ralph Partridge, 9th March 1935): [Firth Erskine’s] Naked Murder and The Plague Court Murders rely too much on fantastic psychology and impossible behaviour to be reckoned as problems for detection. As thrillers they are not without merit and as such they should be read… The Plaque Court victim was murdered during a psychic séance in a haunted house, but readers need not be afraid of ghosts; there is a devilish but human agent at the back of it.
Observer (Torquemada, 10th March 1935): With The Plague Court Murders, Mr. Dickson provides that difficult thing, a second book. The atmosphere of The Bowstring Murders confused me; the atmosphere of this later essay is clearer and satisfyingly Stevensonian. The main problem confronting us is a “Houdini” murder, a physically impossible killing. Mr. Dickson adequately explains the impossible; his novelty, though, is a pleasantly nasty mind.
Spectator (Rupert Hart-Davis, 29th March 1935): The next two books are fantastic, one amusingly, the other nastily so. Bogus spiritualists play an important part in both, while almost everything that happens is wildly improbable… The Plague Court Murders plays yet another variation on the “sealed chamber” or Yellow Room theme. It is neither exciting nor pleasant, and the climax (another preposterous piece of male impersonation) is vastly unconvincing.
Sat R of Lit (2nd June 1934, 40w): Excellent plus.
NY Times (Isaac Anderson, 3rd June 1934, 230w): This is a genuine baffler, placed in an eerie, ghostly setting. Any reader who is able to guess the solution before Sir Henry chooses to reveal it is entitled to call himself a first-class amateur detective.
Books (Will Cuppy, 3rd June 1934, 210w): This thickly atmospheric work provides a sure and pleasant means of giving yourself the jumps, if that is what you crave. In his quest of the eerie, Mr. Dickson works on the principle that too much is enough, so there is no lack of quantity for those who wish to be scared on every page.
Philadelphia Public Ledger: The clever unravelling of the problem is marked by the breaking of one of the most ingenious alibis ever devised.
Daily Telegraph: I need say no more of The Plague Court Murders than that it is a most exciting tale, half thriller, half detective story, with a cunningly manipulated supernatural background, and that it kept me in my armchair till I had finished it.