Peter Diamond—John Wigfull

Peter Diamond and John Wigfull’s professional relationship turns investigation into a contest of interpretations and jurisdiction. Their rivalry is sharp enough to produce teasing and disagreement, but not so rigid that either man cannot recognize the other’s sound work. As the inquiries into the stamp theft and the murders intersect, they repeatedly test each other’s theories; the final balance is not a simple reconciliation, but Wigfull’s candid acknowledgment that Diamond has outdone him.

A rivalry built around the cases

When Wigfull approaches during a discussion of the second riddle, Diamond cuts the conversation short to hear what he has to say. Wigfull has been working on the riddle’s final lines, which direct the reader to a lady in a locked room at number seventeen. Diamond jokes at Wigfull’s expense while making the officers nearby quiet down so the chief inspector can be heard. The exchange establishes their familiar mix of rivalry and attention: Diamond needles his colleague, but gives his deduction the floor.

The riddle points toward the Penny Black’s appearance at the Bloodhounds meeting. Diamond argues that the stamp’s return was planned, that Milo Motion had been selected as the fall guy, and that the thief must have known Milo would bring the book and open it at chapter seventeen. Wigfull and Julie Hargreaves recognize the implication: the person responsible must have known about Milo’s plan, narrowing the field. Diamond immediately resists treating that narrow circle as settled. He insists that the murder belongs to him and warns Wigfull not to interfere, then enlarges the list of possible suspects to include Sid Towers and anyone who had learned what Milo intended to take to the meeting. Their contest is therefore not just over who has the better clue; it is also over how far a clue licenses the investigation to reach.

Competing claims to the locked room

The division between their cases becomes more explicit when Wigfull later summons Diamond to discuss his apparent breakthrough in the stamp theft. Diamond has returned to Manvers Street Police Station after taking Julie to the postmortem when he receives the urgent message. Though he generally avoids Wigfull and expects a dispute over responsibilities, he responds. Wigfull says he believes he has identified the stamp thief and invites Diamond to join him and Arnold Musgrave. Diamond is genuinely surprised, but offers sincere congratulations rather than dismissing the claim out of hand.

Wigfull’s explanation also addresses the locked-room puzzle aboard Milo Motion’s boat. His theory gives Sid Towers a spare key and proposes that Towers could visit the boat at any time. Arnold Musgrave calls the mystery solved; Diamond awards Wigfull full marks and accepts that the explanation has no obvious flaw. Yet Diamond adds a remaining problem: the key was not found on Towers’s body, so the murderer must have taken it. Wigfull promptly allows that the killer could have been a woman. Even at the moment of apparent agreement, their exchange keeps the explanation open to further questions.

That provisional success collapses when Diamond establishes that the keys are Milo’s originals. The padlock therefore was not substituted as Wigfull’s theory required, and the detectives have been working from a false assumption. Diamond does not appear discouraged by the correction; he tells Julie that Wigfull’s theory no longer works and jokes that Wigfull is in deep trouble. The reversal is an important measure of their relationship: Diamond is willing to take pleasure in the competitive setback, but the error is tested against physical evidence, not settled by rank or confidence.

Different conclusions, shared uncertainty

Later, Wigfull draws a neat distinction between their progress: Diamond has his murderer, while Wigfull has his locked-room thief, and the remaining question is how the crime was done. He assumes Rupert Darby is the culprit. Diamond tells him that he knows how the locked room was achieved but does not know who did it, directly challenging Wigfull’s confidence in Darby. This disagreement keeps method and identity separate: solving the apparent mechanics of a crime does not, for Diamond, prove who committed it.

Diamond’s confidence in the method comes from sustained reconsideration, including a flash of inspiration the previous evening and a question from Julie about what the murderer was doing there. Wigfull, by contrast, blushes when Diamond asks whether he really shares the assumption about Darby. Their exchange leaves the identity question unresolved between them at that point. It also shows that their competition does not eliminate uncertainty: each man can claim progress while still lacking a complete account.

Recognition after the solution

When Diamond has Mrs. Shaw brought in, Wigfull finds him in the canteen and has heard that he has cracked the case. Wigfull links the arrest of Mrs. Shaw and her boyfriend to the murder of Darby, reasoning that two people must have worked together when Darby was hanged from the bridge. Diamond is eating after going without food since breakfast and offers no immediate case rundown. Wigfull nevertheless voices his assessment of the evidence and, after hearing the explanation, admits that Diamond is better than he is. The admission marks the clearest change in their rivalry: Wigfull’s competitive interest remains, but he can state plainly when Diamond has solved what he could not.

Their working relationship remains open-ended rather than ceremonially resolved. After conceding Diamond’s success, Wigfull asks whether A.J. is really Miss Chilmark’s long-lost son. The question turns them from the solved case toward another uncertainty, preserving the pattern that has shaped their exchanges throughout: one investigator presses for an answer, the other must decide whether the available evidence warrants it. Their rivalry gives the investigations a second contest alongside the criminal one, but its final note is professional respect earned through correction, persistence, and the recognition of a better deduction.