James Answell has been accused of murdering his fiancee's father, Avory Hume. The case is quite grim: the murder occurred in Hume's study, where every window and the sole door was bolted—not merely locked!—from the inside. There were no secret passages, and absolutely no gaps in any of the entrances. The murder weapon was an arrow that had been hanging in the study, and the only fingerprints on it are Answell's. Answell claims that this was a set-up and that he drank tampered whiskey... but the decanter in Hume's study is full, all the glasses are dry, and the doctor who checks Answell concludes he wasn't drugged.
Despite these overwhelming circumstances, one man believes in Answell's innocence—Sir Henry Merrivale—and takes up his defense in court.
