During a freezing December in the Thames Valley, Hollywood actress Marcia Blystone travels to White Priory, the country estate of Maurice Bohun, a theatrical impresario and antiquarian. Bohun has convened an eccentric house party consisting of his brother, several theatrical colleagues, and personal associates to negotiate production rights. The focal point of the estate grounds is the Queen's Mirror, an isolated, octagonal historical pavilion built in the seventeenth century, situated in the center of an expansive open lawn covered by an unblemished layer of fresh winter snow. In the early hours of the morning, Marcia Blystone is discovered bludgeoned to death on the pavilion floor. Physical inspection of the surrounding terrain reveals an insoluble environmental puzzle: several inches of snow fell during the night, ending well before the estimated hour of death, leaving the expanse surrounding the pavilion completely undisturbed. Only a single track of footprints traverses the lawn from the main house to the pavilion door, and these match the victim's evening shoes precisely. No other footsteps, ski tracks, vehicle marks, or aerial contrivances exist within fifty yards of the structure, leaving no observable physical route by which a human assailant could approach or withdraw from the scene. Chief Inspector Humphrey Masters of Scotland Yard arrives to find local constabulary efforts impeded by the apparent impossibility of the physical footprint evidence. Accompanied by American diplomat James Bennett, Masters requests the intervention of Sir Henry Merrivale, whose investigative approach emphasizes practical mechanics and thermodynamic analysis. With the suspects confined to the estate and mutual accusations mounting among the theatrical company, Merrivale must determine the exact timing of the weather conditions and deduce how an external weapon could inflict fatal blunt-force trauma across an untouched snowfield.

US: The Punch and Judy Murders

US: The Peacock Feather Murders

US: The Crossbow Murder

James Caplon Answell visits the London residence of Avory Hume, a former diplomat and prominent sporting authority, to formally seek permission to marry Hume's daughter, Mary. Answell is an athletic young man of unblemished reputation with no known enmity toward the Hume family. Hume receives him into his private ground-floor study, an interior designed as an impregnable security room containing a collection of historical arms and an extensive cellar. After exchanging brief introductory remarks, Hume pours drinks for both men and fastens the room's access points. Moments after consuming his whiskey, Answell experiences severe vertigo and loses consciousness, having ingested a fast-acting sedative. Upon waking, he finds Hume lying dead before the fireplace, pierced through the heart with an arrow taken from a pair of antique crossbows mounted upon the study wall. The mechanical security of the chamber is absolute: the heavy oak door is secured from within by two solid steel bolts, the windows are sealed by bolted interior iron shutters, and the hearth chimney is blocked by a permanent iron grate. Only Answell and the deceased occupy the room, and Answell's fingerprints alone are recovered from the shaft of the crossbow bolt. Arrested on capital charges, Answell is committed for trial at the Old Bailey, where the prosecution constructs an apparently unassailable circumstantial case under Senior Treasury Counsel Sir Walter Storm. With the defendant facing execution, defense solicitor Arthur Bailey enlists Sir Henry Merrivale, the cynical barrister and former head of the Secret Service's counter-espionage division. Taking his place at the defense table, Merrivale mounts a high-stakes courtroom defense founded upon a specific physical premise: that every locked chamber contains an overlooked opening—a 'Judas window'—through which an external assailant could strike without breaching the room's physical boundary.

US: Nine - And Death Makes Ten

US: Death and the Gilded Man

US: The Curse of the Bronze Lamp