In most of his adventures, Sir Henry Merrivale seeks to show that someone could have done an apparently impossible deed. In this outing, his foremost objective is to prove that someone did not commit an apparently obvious crime.
The standard locked-room mystery posits a situation in which no one (it seems) could have entered a given space at a given time. But here’s the situation that investigators confront in the murder of Amory Hume: One man and only one man (it seems) visited Hume in his study at a certain hour on a certain Saturday evening. That man and only that man (it seems) was present when an arrow fired at close range struck Hume dead in that room and at that hour. The man in question—the man who, in effect, wears a bull’s-eye of guilt on his back—is James Caplon Answell. He’s an amiable young chap who plans to wed Hume’s daughter. In his telling, he walked into the study, met the victim-to-be, was knocked unconscious by a drugged serving of whiskey, and shortly thereafter awoke to find Hume’s corpse lying nearby. For Answell, the whole affair isn’t a locked-room mystery; it’s a locked-in mystery. Apart from a brief prologue, he spends the entirety of this tale in the dock at the Old Bailey, where he is on trial for murder. Court officials call him, simply and chillingly, “the prisoner.” His one bit of good fortune is that Merrivale is at the Old Bailey, too, appearing as counsel for the defense.
Despite its atypical structure—it unfolds as a courtroom drama, with most of the standard investigative action taking place off-stage or in the recent past—Judas Window contains everything that an enthusiast of the classic locked-room novel might want. It’s a mid-career work that shows its author (John Dickson Carr, writing under the least mysterious of pen names) at the height of his powers. Like all great works of this type, it combines complexity and simplicity. Information regarding the arrangement of the crime scene, the movements of each suspect, and the potential significance of each clue gels into a pattern whose intricacy is devilish or heavenly, depending on your taste for that sort of fare. Yet the solution to the core riddle is one that you could jot down on the back of a postcard.
In Carr’s masterfully structured plot, every clue becomes an arrow that might point in any number of directions. From various angles, Merrivale and other characters examine the known points of entry to the murder chamber. He and they entertain multiple theorized solutions. At each turn, the brute facts of the matter appear to reinforce the edifice of impossibility that surrounds Answell’s claim of innocence: The sole door to Hume’s study, a heavy wooden thing, was bolted from the inside at the time of the murder, while the windows were encased in iron bars that show no sign of tampering. Then, midway through the trial, Merrivale begins teasing courtroom attendees with the notion that the study contains a “judas window”—an unseen opening that might have allowed someone other than Answell to kill Hume. The notion, as Merrivale initially presents it, conjures up supernatural possibilities. In a climactic moment, however, he demonstrates to the court that the aperture in question is as prosaically real as the powdered wig on a judge’s head.