The narrative follows a sequence of mysterious deaths within a wealthy family's mansion that confound police and the public; an urbane amateur detective applies forensic detail, psychological analysis, and careful reasoning alongside official investigators to unravel staged scenes, missing weapons and poisons, locked-room puzzles, and misleading traces. As successive tragedies escalate tension, methodical reconstruction of timelines, attention to small physical clues, and probing of motives expose an unexpected mechanism and the perpetrator's ingenuity, culminating in a logical but startling explanation of how the crimes were committed and why.