A Most Agreeable Murder

The novel is set in Swampshire, a small English township governed by a rigid code of etiquette established by its founding father, Baron Fitzwilliam Ashbrook, and codified in The Lady's Guide to Swampshire. Women who violate these rules face permanent social disgrace and exile. Beatrice Steele, the witty eldest daughter of the Steele family, secretly defies this code by obsessing over crime-solving, following cases through Sir Huxley's crime column in imported London newspapers and writing him anonymous letters signed only with her initials.

Beatrice's family faces a dire threat. Their estate, Marsh House, can only pass to a male heir; if none of the three Steele daughters marries and produces one, the home goes to their repulsive cousin, Mr. Martin Grub. Beatrice's mother, Mrs. Susan Steele, pins her hopes on Louisa, the beautiful middle daughter. The youngest, Mary, is withdrawn and mysterious. When Louisa announces that the wealthy Mr. Edmund Croaksworth will attend the Ashbrooks' autumnal ball, Mrs. Steele throws the household into frantic preparations. A legal petition also arrives from Grub seeking to declare Mr. Stephen Steele, Beatrice's prankster father, mentally unfit and seize Marsh House.

On the way to the ball at Stabmort Park, the Ashbrook family estate, the Steeles encounter a scarred, eye-patched stranger in the storm. Beatrice recognizes him as Inspector Vivek Drake, Sir Huxley's former investigative partner, disgraced after the two clashed over a murder case involving Viscount DeBurbie. Drake reveals he is traveling with Croaksworth on business and states Croaksworth is not seeking a wife.

At the ball, Beatrice notices a muddy boot print containing wild honeysuckle, a plant found only at Adler's End, a forbidden wooded area at the estate's boundary. She also sees a silver spoon with a dog-shaped handle fall from Drake's cloak. Inside, she reconnects with Daniel Ashbrook, the Stabmort heir and her oldest friend. Daniel hints at romantic feelings, but Beatrice feels no spark. Croaksworth arrives and gravitates toward Louisa.

During a break, the men retire to the study for cards while the women play whist. Daniel's sister Arabella, the ball's hostess, proposes playing for secrets instead of money. When the men return, Louisa hastily burns all the written secrets. During an elaborate Italian dance called the danza della morte, Croaksworth begins convulsing. He coughs blood onto Louisa's gown and shouts, "The angel isn't an angel at all" (96). He collapses and dies. Beatrice and Drake identify his symptoms as signs of poisoning. The storm traps all the guests, and Hugh Ashbrook, Daniel's father, appoints Drake to investigate, with Beatrice as advisor and Miss Helen Bolton, a wealthy older neighbor, as chaperone.

Beatrice discovers a trapdoor in the study leading to a hidden underground card room. She and Drake find a scorecard with the initials C, C, A, and F; a trick deck bearing a purple iris design; and a partially burned IOU. They question the guests. Daniel claims he spent the break alone. Hugh Ashbrook claims memory loss and reveals that Arabella and Croaksworth were once engaged. Caroline Wynn, considered Swampshire's most accomplished woman, is caught in lies about her whereabouts. Frank Fàn, a notorious rake, denies involvement despite the "F" on the scorecard and insinuates Louisa had a prior relationship with Croaksworth. When Drake notes that belladonna, a plant Louisa uses as a cosmetic eye-drop, is also a fatal poison, Louisa becomes nauseous and flees.

Beatrice is attacked by a cloaked figure who tries to strangle her. She stabs her earring into the assailant's wrist and escapes. Noting that her attacker wore rough gardening gloves and that belladonna grows in Arabella's greenhouse, she and Drake investigate the greenhouse. Hidden among the plants, they overhear Captain Philip Peña, a naval officer and Caroline's former suitor, confess his love to Caroline and admit he lied: Caroline, not he, was the fourth card player. Beatrice also finds an empty belladonna vial labeled with Louisa's name and hides it, terrified Drake will accuse her sister.

A decoy carriage lures them to Adler's End, where Drake falls into a squelch hole, a deep mud sinkhole, and Beatrice saves his life. Back at the house, Drake presents his case at dinner. He exposes Frank's trick deck, reveals that Frank and Louisa are secretly engaged and expecting a child, and accuses them of murdering Croaksworth to claim his fortune. Louisa and Frank insist they are innocent: Their plan was to lie about the child's parentage, but they killed no one. Beatrice notices Hugh Ashbrook wearing gardening gloves matching her attacker's and accuses him. Captain Peña pulls away Ashbrook's blanket to reveal his throat has been slit, a knife in one hand and a confession note in the other.

The case appears resolved, but Beatrice is attacked again and nearly drowned in the bath room. Louisa, who earlier accused Beatrice of selfishness for refusing to marry and burdening the family, saves her with a candlestick. The sisters tearfully reconcile, and Beatrice confesses she wants to be an inspector, not a proper lady. She realizes the killer must still be at large since the attack came after Ashbrook's death.

She finds Drake handcuffed to a settee by Caroline, who holds a stolen cutlass to his throat. Drake reveals Caroline is actually Verity Swan, the suspected accomplice in the DeBurbie murder, living under aliases in Swampshire. Her emerald choker contains DeBurbie's stolen jewels. Caroline escapes with Captain Peña, though Beatrice pickpockets the choker.

Drake finds the hidden belladonna vial and accuses Louisa again. Beatrice handcuffs him and destroys the vial, vowing to prove her sister's innocence. In the study, Daniel saves Beatrice from Grub and proposes marriage. But Beatrice spots a scratch on Daniel's wrist, the mark her earring left on her attacker, and accuses him of murder.

Daniel confesses. The Ashbrooks are bankrupt: After his mother's death, Hugh spent their fortune on quack remedies. Daniel secretly married Alice Croaksworth to access her family's wealth, but Alice's parents cut her off, and Daniel imprisoned her in a sealed turret. When Croaksworth recognized the paper Daniel used for scorekeeping as matching Alice's farewell letter, he confronted Daniel. Daniel poisoned Croaksworth with belladonna from his father's tonic cabinet, then killed Hugh with a sharpened quill and forged a suicide confession. He planted all the evidence framing Louisa and his father. Croaksworth's dying words were a warning about Daniel, the seemingly perfect gentleman.

Daniel sets the study ablaze and locks Beatrice inside. She picks the lock using instructions from an architecture book Daniel had lent her. Drake, freed by Mary, meets Beatrice in the mansion's secret tunnels. Together they ascend to a sealed turret and find Alice alive, imprisoned for two years. Daniel tries to escape through a window using a quilt Beatrice had once sewn, but her notoriously bad stitching tears apart, and he plummets to his death. With the mansion burning, Miss Bolton arrives on the rooftop with a silk parachute hidden in her hat, and all four leap to safety.

Three months later, Louisa and Frank marry, and the community begins rethinking its rigid etiquette. Grub is arrested for Beatrice's attempted murder, disqualifying him from inheriting Marsh House. Arabella plans to move to Paris to live with Sophie Beaumont, the dressmaker she has secretly loved. Alice Croaksworth, now wealthy as her family's sole survivor, confirms that Drake's father was also her father, making Drake a Croaksworth by blood and his silver spoon a family heirloom. Alice funds a London detective office, and Drake asks Beatrice to be his equal partner. She accepts, and the novel ends with the two walking toward Marsh House, the beginning of their "perfectly exasperating partnership" (306).