The registered envelope from Windle reaches the office, and Mr. Pond opens it, making him a witness. When Miss Murchison bursts into Mr. Urquhart’s room she notices a dark line in the panelling behind his head. After hours she talks her way past the charwoman Mrs. Hodges, finds the sliding panel by accident, and opens the inner cupboard with Blindfold Bill’s keys. Inside are Megatherium Trust certificates showing Urquhart gambled Mrs. Wrayburn’s money, the will, and a foreign chemist’s packet of white powder.

At Wimsey’s flat, Parker lays out the case: Urquhart’s motive is strong, but everything Philip Boyes ate or drank at dinner was shared or tested. Bunter reveals that Hannah Westlock found Boyes’s bedroom water bottle emptied and dried. Then Bunter runs Marsh’s test on Miss Murchison’s sample and a dark ring with a metallic centre forms, confirmed as arsenic. Wimsey reads all night through the notable British trials and by morning announces he knows how it was done.

• Rule 7 of the Cattery: always distrust the man who looks you straight in the eyes
• Miss Murchison teasing Urquhart outside a butcher’s window until he stalks off
• A scrap of silk torn from her own bag as her excuse to Mrs. Hodges
• Freddy Arbuthnot complaining that the chemistry show lacks pep
• The books left open for Bunter, from the Maybrick trial to A Shropshire Lad