Rupert's keyring

Rupert's keyring is a small piece of physical evidence whose apparent promise is tested in the murder squad's incident room. Recovered from Rupert Darby's jacket after his death, it brings Peter Diamond and John Wigfull back to the padlock at the center of the locked-room investigation. Its importance lies not in an immediate solution, but in the exactness of the comparison: similar locks, several keys, and a result that rules out a seemingly obvious match.

Recovery and Contents

After Rupert Darby's body was found, a constable noticed that the padlock among the contents of his leather jacket was the same make as the German padlock featured in the locked-room case. The discovery prompted the incident room to be informed. The keys on a ring were recovered from the same pockets, but they were a separate item from the padlock; the evidence does not establish that any key on the ring belonged to it.

At the incident room, the pocket contents were labeled and bagged. Peter Diamond singled out both the padlock and Rupert's keys for comparison with the lock and key associated with Milo Motion's narrowboat. That move gave the keyring a specific investigative role: it could test whether Rupert had possessed a key capable of operating the lock linked to the earlier mystery.

The Comparison in the Incident Room

John Wigfull handled the bag containing the keys by shaking them onto the table, avoiding direct contact with them. The room's work stopped as detectives and other staff gathered to watch Peter Diamond's test. The ring held four keys: one Yale-type key that looked like a front-door key, one plastic-topped key thought likely to be for a car, and two small, narrow keys identical in shape.

Peter Diamond tried each of the two narrow keys in the lock from Milo Motion's narrowboat. Neither would turn it. John Wigfull took this as confirmation that the keys did not match and proposed comparing one with Milo Motion's key. Placed side by side, the keys were visibly cut for different locks. The test established a precise negative result: the two small keys on Rupert's ring did not open that padlock, and they were not copies of Milo Motion's key.

Evidentiary Significance

The keyring complicates rather than resolves the first impression created by the matching make of the padlock. A padlock of the same make in Rupert's pocket could appear to connect him to the lock under investigation; the presence of several keys could seem to offer a route to proving that connection. But the controlled comparison does not support the simple theory that one of Rupert's two identical narrow keys operated Milo Motion's lock.

That failure does not, by itself, identify what the keys opened or explain why Rupert carried them. Nor does the comparison settle the broader locked-room question. Peter Diamond remains undiscouraged and begins setting out how the lock was used, while the keyring's demonstrated contribution is narrower: it lets the room distinguish a visible resemblance from a working key. In a case built around the apparent security of a padlock, that distinction makes the ring a useful test of the evidence, even though it supplies no self-sufficient answer.