Murder of Sid Towers aboard Milo's narrowboat

The Murder of Sid Towers aboard Milo’s narrowboat is presented not only as a killing but as a locked-room problem that resists an apparently secure chain of physical facts. When Peter Diamond returns to the boat with Milo Motion, forensic examination has found no flaw or tampering in its high-security padlock; Milo’s key, the locked stern door and a second door bolted from inside seem to leave no way for the killer to have entered and departed. The evidence makes the mechanism look reliable, but it cannot establish that Milo’s account is true. The puzzle therefore turns on the difference between what the hardware proves and what a witness says happened.

Return to the boat and search for a weapon

Later that afternoon, Diamond drives Milo to the Dundas Boatyard so he can collect a change of clothes from the Mrs. Hudson. The Scenes of Crime team has finished its work. Police activity has dwindled to one cold constable and two divers searching the canal for the murder weapon. In water too shallow for proper diving, they wade and bend double, retrieving an unlikely inventory: a horseshoe, plastic milk crates, a bicycle pump, a birdcage, about twenty beer cans and pieces of stone. The finds are the result of three hours’ work along fifty yards of canal either side of the narrowboat.

Diamond ends the search for the day. He considers it unlikely that a killer capable of such an artful crime would discard the weapon in the obvious stretch of water, but the search had to be made. Rather than treat the lack of a recovered weapon as a solution, he asks Milo to inspect the boat for anything missing that could have been used to strike Sid over the head. Milo cannot immediately think of such an object, though he agrees to look. The request keeps open the possibility that the weapon came from aboard the boat without establishing that it did.

The lock and the closed cabin

The stern door has a fresh lock, so a constable must open the boat for Diamond and Milo. The original German-made padlock has been dismantled and examined at the forensic laboratory. The scientists report no defect and no sign of tampering. It is a high-security close-shackle model, with more than six million possible key variations; according to the manufacturer’s claim, every padlock sold in Britain has a unique key pattern. The examination thus gives Diamond no mechanical weakness to explain the apparent entry into, or exit from, the cabin.

Diamond has already turned the boat’s security arrangements over repeatedly in his mind. The extra inspection brings little confidence that he will find an answer. He thinks of Sid’s murder as his own locked-room mystery, a Gordian knot, and sets out the conditions that follow if Milo has told the truth: Milo locked the boat when he left; the key stayed on his person; his keys fitted that padlock and no other, and there was no second key; the only other entrance to the cabin, at the fore end, was bolted from inside; and, when Milo returned with John Wigfull, the padlock was still in place until Milo opened it and found Sid’s corpse inside.

These details make the apparent impossibility precise. The stern lock was not simply found secured: it was still there when Milo returned, and he says he opened it with the key he had kept. Nor does the fore-end door offer an obvious alternative route, since it was bolted from within. Yet Diamond’s reasoning repeatedly arrives at the same qualification: the facts hold if Milo spoke truthfully. The laboratory can test the padlock; it cannot verify the key’s whereabouts or the accuracy of Milo’s account. The more intact the security appears, the more sharply the human testimony becomes part of the puzzle.

Sid’s unexplained visit

The physical problem is only one part of Diamond’s inquiry. He also asks why Sid came to the boat at all. Milo says Sid was not in the habit of visiting him and knew that he would be away: Milo had told everyone he was going directly to the police station to hand in the stolen Penny Black stamp. Milo raises the possibility that the murderer lured Sid there, but Diamond declines to continue trading theories and sends him to choose the clothes he needs while Diamond walks along the towpath.

Milo’s earlier view of the other Bloodhounds offers a contrast rather than an answer. He describes the group as charming, says that Miss Chilmark is better than her sour reputation suggests, and recalls Jessica Shaw helping Sid fit in and taking him for drinks more than once. In Milo’s judgment, the members are unlikely suspects, and he can think of no one with a grudge against Sid. That confidence does not explain Sid’s arrival at the Mrs. Hudson, however; nor does it resolve whether he came by invitation, by deception, or for some reason not yet known.

Significance of the unresolved puzzle

The episode separates a locked door from a solved crime. The lock’s elaborate security and clean forensic report might seem to close off ordinary explanations, but they instead narrow Diamond’s attention to the unverified human sequence around it. The weapon remains unrecovered, the object that may have caused Sid’s fatal head injury has not been identified, and the motive for Sid’s visit remains unsettled. By placing those unanswered questions beside a numbered account of the cabin’s security, the narrative makes the murder’s central contradiction legible without prematurely resolving it: the boat appears to have been locked, while a body was found inside.