Windlass aboard the boat

The Windlass aboard the boat is the blunt weapon used to kill Sid Towers, and its role links the apparent locked-room puzzle to the violence that follows. Before the killer is identified, Peter Diamond considers whether Polly Wycherley could have wielded it; the later reconstruction places it in A.J.'s hands inside the cabin, where a panicked blow kills Sid and transforms the riddle into a murder investigation.

A possible weapon and a line of suspicion

While questioning Polly Wycherley about Sid's death, Peter Diamond weighs whether she could physically have struck him with a windlass. He considers a blow delivered from behind or while Sid was bent forward, and notes that the pathologist reported a couple of blows. This is a test of possibility, not proof: Diamond is still assessing Polly's opportunity and motive, and the weapon's presence does not establish that she used it.

A.J.'s use of the windlass

Diamond later reconstructs a different sequence. A.J. was replacing the padlock when Sid approached along the towpath; hearing him, A.J. hid inside the cabin and grabbed a windlass as a weapon. The planned deception had been working, but Sid's arrival provoked fear and anger. Diamond believes A.J. probably meant only to knock Sid unconscious; the blow instead killed him.

From puzzle to murder

The windlass marks the point at which A.J.'s elaborate padlock trick ceases to be merely a staged mystery. Sid's fascination with the locked-room puzzle brings him to the boat, and the weapon A.J. seizes to protect his scheme produces a death he then has to conceal. Its role also explains why the early possibility that Polly had wielded it is misleading: the decisive account identifies A.J. as the person who struck Sid.