The locked-room mystery aboard Motion's boat

The locked-room mystery aboard Motion's boat is a double puzzle: a stolen Penny Black appears inside Milo Motion's book, and Sid Towers's body is found inside Motion's narrowboat after it has apparently remained locked. The boat's security gives the mystery its physical form, while the book and the stamp connect it to an earlier theft. At this stage, the questions are sharply framed but not answered: how did anyone enter the boat, and when did the stamp get into the book?

Two mysteries, one boat

Peter Diamond identifies two distinct problems rather than treating the case as a single locked-room trick: the mystery of the stamp and the mystery of the murder. The Penny Black was found between the pages of Milo Motion's copy of The Hollow Man, a book he kept on a shelf aboard the boat. Motion says he had no visitors during the preceding week. On the evening of the Bloodhounds meeting, he took the book from the shelf and kept it in his possession throughout; John Wigfull had already established that nobody at the club had an opportunity to put the stamp inside it.

That account shifts the likely point of insertion back to the boat. If the Penny Black was already in the book when Motion took it from the shelf, whoever planted it must have boarded the narrowboat, got inside, and found the book. Wigfull presents this as the likely sequence, not as a demonstrated solution. The distinction matters: the club can be excluded as the place where the stamp was planted, but that does not explain how an intruder crossed the boat's security or establish precisely when the stamp entered the book.

The title of Motion's book sharpens the coincidence. The missing stamp was found at the start of a chapter called The Locked-Room Lecture, and the boat itself now appears to present a locked-room puzzle. Diamond's response is to keep the two mysteries in view: an apparent literary echo does not settle either the murder or the theft. The stamp may have been a tactical move in a more serious game, but he treats that connection as a possibility rather than a proven motive.

The discovery and its chronology

Motion left his boat at a quarter to seven to attend a meeting in Bath. Sid Towers, a forty-six-year-old night watchman, was last seen alive in the centre of Bath at eight forty-five that evening. At about one in the morning, Motion returned with Wigfull. The boat was still padlocked, as Motion had said it would be; when he opened it, the two men found Towers's body on the lounge floor. Wigfull was the person who discovered the body, but Motion's opening of the boat supplies the crucial visible circumstance: the victim was inside while the outside lock had remained in place.

The death makes the puzzle more than an ingenious arrangement around a missing stamp. Towers had been struck on the head with a heavy object, possibly a spanner, and the weapon had not been found. Divers were searching the water in case it had been thrown there, although Diamond doubted that the killer had disposed of it in that way. The account therefore provides a likely kind of weapon, not an identified one or a confirmed disposal method.

The two timelines overlap without yet explaining one another. Motion's absence creates the interval in which the intruder would have had to enter if the Penny Black was planted aboard; Towers's last known sighting and the later discovery place the murder within the same evening. The police state that there seems to be a link between theft and murder, but the available facts leave the nature of that link open. The boat's locked condition is the shared problem that gives both crimes their connection.

The boat as a secured space

The narrowboat is about sixty-five feet long. Its cabin area has no hatches, and its windows offer no entry route beyond a narrow vent at the top. There is a door at each end. When Motion is aboard, he says, he bolts the doors from inside; when he leaves, he secures the boat from outside with a padlock. Diamond and Wigfull have seen the interior bolts, including Chubb security bolts at the top and bottom of one door. The other is held by a close-shackle padlock.

The padlock's key history makes the external barrier more specific. Motion says there were originally two keys, but one fell into the canal at least a year earlier, leaving him with one. He describes the lock as strong, expensive, German-made, and bought from a locksmith in George Street; he also argues that a similar key could not simply be bought in England. The remaining key is on a ring in his pocket. The account supplies a claimed single-key security system, although the claim itself does not identify who could have opened the lock or how.

When Diamond examines it, the heavy-duty steel padlock is unlocked and hooked over an iron staple at the top of the door. With the door shut, the staple would pass into a hinged metal strap attached to the sliding hatch at the rear of the roof. Diamond regards the arrangement as secure-looking but does not touch it, waiting for the Scene of Crime Officers. This inspection records the lock's condition without claiming that the visible arrangement alone solves the entry problem.

The limits of the locked-room claim

The mystery rests on a conflict between Motion's reported routine and the crime scene. He insists that nobody was aboard when he left and that he bolts himself in whenever he is aboard. Wigfull says the boat was padlocked when they arrived, just as Motion had claimed. Together, these statements make the discovery appear to rule out ordinary entry, but they remain reported circumstances, not a complete reconstruction of the killer's movements.

A possible route through disturbed door fittings is raised by Keith Halliwell. Diamond answers that the padbar and staple have rusty screws and show no scratches indicating recent interference. That observation narrows one proposed explanation: there is no visible sign that the fittings were recently unscrewed. It does not, by itself, disclose how the killer entered or how the Penny Black was planted.

The boat thus functions as both a home Motion says he keeps secure and a puzzle space whose apparent closure has to be tested against physical evidence. Its locks, bolts, key, restricted windows, and intact-looking fittings give the police concrete details to examine, while the body's presence prevents the problem from remaining a literary game. The available account sustains the locked-room condition as an unresolved investigative question: the boat was secured when Motion and Wigfull returned, yet Towers was inside, and the evidence presented here has not established the means.