Padlock on the Mrs. Hudson

The Padlock on the Mrs. Hudson is the boat’s heavy-duty exterior lock, and its apparent exclusivity makes it the central obstacle in the investigation’s locked-room puzzle. Milo Motion says he keeps its only surviving key on his key ring, while the police examine the lock and its fittings without finding signs of tampering. Yet the Penny Black is found inside Motion’s copy of The Hollow Man, and investigators conclude that whoever planted it must have gained access to the locked boat. The padlock turns an ordinary act of securing a boat into a test of what the witnesses know, what the evidence proves, and whether the barrier was as absolute as it seemed.

Purpose and Physical Arrangement

Motion describes the lock as a substantial security device. When asked whether he secures the boat while away, he says that he does, displaying the key from his pocket and explaining that he carries it on his key ring. He presents the lock as exceptionally difficult to duplicate: according to his initial account, the retailer guaranteed that no similar key had been sold from the same shop, which he describes as the only seller of such locks in the west of England. The lock’s importance rests not only on its strength but on the claimed uniqueness of its key.

The investigators later inspect the lock in place. It is a steel padlock, unlocked when Peter Diamond examines it with a torch and hooked over an iron staple fixed to the top of the door. When the door closes, the staple fits into a hinged metal strap attached to the sliding hatch at the back of the roof. Diamond regards the arrangement as secure and refrains from touching it until the Scene of Crime Officers arrive. This caution matters: the lock is not merely a puzzle prop but physical evidence whose condition must be preserved.

The padlock protects one of the boat’s two entrances. In Diamond’s account, the cabin area is about sixty-five feet long, has no hatches, and cannot be entered through its windows, which have only a narrow vent at the top. One door is secured from inside by Chubb security bolts at the top and bottom; the other is locked from outside with the close-shackle padlock. Motion says that he uses the external lock when he is away, but, while aboard, he closes the boat and bolts it from within. The two different methods of securing the doors create the conditions for the apparent locked-room problem.

The Key and Motion’s Account

Motion says there were originally two keys. He has only one because the spare fell into the canal at least a year earlier. He further insists that the lock is German-made, strong, and expensive, and that its design makes every lock unique. In the later discussion, Diamond says the locksmith confirmed that another key could not simply be bought for it. The surviving key, Motion’s possession of it, and the missing spare together narrow the apparent means of entry while leaving the investigators to explain how anyone could have reached the boat’s interior.

The accounts of where Motion obtained the lock do not match exactly. When first showing the key, he names Foxton’s; later, he identifies a locksmith in George Street. The passages do not explain the difference. Both accounts support his broader claim that the lock is unusual and difficult to duplicate, but the discrepancy remains part of the record rather than a detail the investigation resolves here.

The Lock as Evidence in the Mystery

The first problem is the Penny Black’s appearance inside the book. Wigfull says he established that nobody at the club had an opportunity to put the cover there. Since Motion says the book had remained on a shelf aboard the boat and that he had no visitors during the preceding week, the stamp must have been planted before he took the book to the Bloodhounds meeting. Diamond reasons that the perpetrator must therefore have boarded the boat, entered it, and found the book. The padlock is the obstacle that makes this explanation appear impossible.

Possible methods of bypassing it are tested against the physical evidence. Keith Halliwell suggests removing the padbar and staple, but Diamond says the screws are rusty and show no recent interference. An attack on the hinges is also considered; they are inaccessible from outside and have not been tampered with. Diamond invokes the categories of lock interference discussed in The Hollow Man: manipulating a key from the wrong side, removing hinges, or tampering with an interior bolt. He dismisses those routes for this boat, especially because the internal bolts are recessed finger-bolts rather than the exposed, primitive devices described in the book. If Motion is not the culprit, Diamond concludes, the person who planted the stamp must have found a way to undo the exterior padlock.

That conclusion clashes with the apparent certainty of the lock’s security. Wigfull insists that bypassing it is impossible because the sophisticated lock has only one key and Motion kept that key throughout questioning. But Wigfull also reports watching Motion use the key at the boat: he had his torch pointed at the lock, saw Motion take the key from his pocket, heard a click, and saw the shackle spring open. The observation establishes that the padlock was unlocked with Motion’s key; it does not, by itself, reveal how the stamp had earlier been planted. The distinction between witnessing the lock open and accounting for the earlier access keeps the puzzle alive.

Narrative Significance and Unresolved Questions

The padlock’s force in the story comes from the mismatch between material certainty and investigative uncertainty. Its steel body, staple, strap, rusty screws, inaccessible hinges, and unique-key claim invite close inspection, while each apparently ruled-out route makes the remaining explanation harder to find. The lock changes from a routine convenience into a conspicuous object: its security is repeatedly asserted, but the crime inside the boat requires investigators to challenge what that assertion can establish.

The riddle has two related forms. The Penny Black’s presence in the book demands an account of how an outsider entered the boat; the murder investigation also raises the broader question of how the secured cabin could be accessed. Diamond explicitly distinguishes the mysteries of the stamp and the murder, while allowing that the theft may be a tactical move in a more serious game. In the available account, the padlock is not yet explained away. It remains the hard, visible boundary around the boat—and the point where the evidence’s apparent certainty gives way to an unanswered problem.