Harriet Vane
Mystery novelist on trial for murdering her former lover; candid, wounded and proud, she refuses to perform contrition for the court or gratitude for Wimsey, turning down his repeated proposals even as he works to save her life. Acquitted at last with her innocence publicly declared.
Lord Peter Wimsey
Aristocrat-detective who decides at first sight that Harriet is innocent and that he will marry her. He funds the defence, deploys his agents, deduces the arsenic-immunity trick from his library, and springs the trap that exposes the real killer — then leaves without collecting thanks.
Norman Urquhart
Boyes's cousin, a sleek Bedford Row solicitor and the murderer. Having embezzled his great-aunt's trust money in the Megatherium crash, he immunised himself to arsenic over two years, poisoned the shared omelette via a cracked egg, staged a suspicion-proof dinner, and forged a will draft to mislead Wimsey.
Philip Boyes
The victim, an advanced novelist of small sales and large vanity who demanded devotion, tested Harriet by offering marriage as a prize, and died of arsenic believing to the end that she hated him. Unknown to himself, the true heir to Mrs. Wrayburn's fortune — which is why he had to die.
Miss Katharine Climpson
Spinster head of Wimsey's typing bureau who, as a juror, forces the hung jury that saves Harriet. Sent to Windle, she fakes seances with a soapbox clicker and wire hooks to manipulate a spiritualist nurse, finds Mrs. Wrayburn's real will, and steams it open with her conscience protesting throughout.
Miss Joan Murchison
Bureau operative planted as Urquhart's typist. She spots the telltale typewriter that exposes the forged draft, learns lock-picking from Blindfold Bill, opens the Wrayburn deed box, and finds the embezzlement papers and the arsenic packet hidden behind the office panelling.
Bunter
Wimsey's incomparable valet, who charms the dinner details out of Urquhart's cook and parlourmaid over crumpets, deduces his master's feelings before anyone else, and performs the Marsh test that proves the hidden powder is arsenic.
Chief Inspector Charles Parker
The Scotland Yard man who built the case against Harriet and is honest enough to help dismantle it. He traces the pub powder, accepts the case against Urquhart, makes the arrest — and, after prodding from Wimsey, finally proposes to Lady Mary.
Mrs. Wrayburn (Cremorna Garden)
Harriet-adjacent only by fortune: a scandalous Victorian actress, now over ninety, paralysed and speechless, whose shrewdly hoarded wealth is the engine of the crime. Her 1920 will forgives the Boyes branch and leaves Philip the bulk of everything.
Miss Booth
Mrs. Wrayburn's kindly, credulous nurse-companion, a convinced spiritualist. Miss Climpson's staged messages from her lost sweetheart Harry lead her to open the safe and post the will to Urquhart in good faith.
Hannah Westlock
Urquhart's observant parlourmaid, whose precise testimony about the dinner unwittingly shields the murderer until it becomes the key to convicting him — she remembers the cracked egg Urquhart insisted go into the omelette, and the strangely dry water bottle.
Sir Impey Biggs
Harriet's eminent defence counsel, who secures the hung jury and, at the retrial, insists on a declaration of complete innocence rather than a quiet withdrawal.
Ryland Vaughan
Boyes's devoted hanger-on and literary executor, certain Harriet poisoned his genius out of spite; his grief and his little bottle of poison-in-waiting help Wimsey rule out both him and suicide.
Freddy Arbuthnot
Wimsey's amiably dim City friend, whose financial gossip confirms Urquhart's losses in the Megatherium crash, and whose engagement to Rachel Levy supplies the Christmas chapter's subplot.