The Secret Adversary

The novel opens in May 1915 as the Lusitania sinks after being torpedoed. A nervous passenger named Danvers, carrying secret wartime papers vital to the Allies, entrusts an oilskin packet to a young American woman on deck. He instructs her to deliver it to the American Ambassador if a coded advertisement fails to appear in the Times within three days. She accepts and boards a lifeboat.

Several years later in post-war London, Tommy Beresford, a demobilized young officer, and Prudence "Tuppence" Cowley, the fifth daughter of an archdeacon, run into each other at a Tube station. Both broke and unemployed, they form a partnership called "the Young Adventurers, Ltd." Tommy mentions overhearing strangers discuss someone called Jane Finn. As Tuppence walks home, a shifty man named Whittington approaches, offering work. At his office the next morning, he proposes paying her handsomely to pose as his ward in Paris. When he asks her name, Tuppence impulsively says "Jane Finn." Whittington reacts with fury and fear. Tuppence bluffs her way out with fifty pounds, noting that a clerk named Brown delivers a message during the meeting. When they return the next day, Whittington's office has been abandoned.

Tuppence places an advertisement seeking information about Jane Finn. Mr. Carter, a high-ranking intelligence official, responds and explains the background: In 1915, a draft secret treaty was dispatched from America via Danvers on the Lusitania. Danvers died, but the treaty vanished. Jane Finn, a young American orphan seen speaking with Danvers before the sinking, was listed among the survivors but disappeared after reaching England. The treaty now threatens to discredit British leaders and fuel Bolshevist-backed unrest if published. Behind this threat stands a master criminal known only as "Mr. Brown," who hides in plain sight. Carter hires the pair to find Jane Finn. The second respondent, Julius P. Hersheimmer, is a young American millionaire and Jane's cousin. He reveals that an "Inspector Brown" took the only surviving photograph of Jane, another move by Mr. Brown. Julius joins the search.

Tommy and Tuppence trace a woman named Rita, mentioned in Whittington's office, to Mrs. Vandemeyer at South Audley Mansions. They split up: Tommy follows Whittington's associate Boris to a decrepit house in Soho, bluffs his way inside, and hides behind a curtain to observe a clandestine meeting. Conspirators discuss funding terrorism, manipulating the press, and planning a general strike for the 29th of the month. Their success hinges on a document connected to "a girl." Tommy is knocked unconscious before learning more. Meanwhile, Tuppence goes undercover as Mrs. Vandemeyer's parlormaid, confirming her involvement in the conspiracy. Sir James Peel Edgerton, a celebrated barrister and criminologist associated with Mrs. Vandemeyer, visits the flat and cryptically warns Tuppence to leave.

With no word from Tommy, Tuppence and Julius enlist Sir James to question Mrs. Vandemeyer. Before he arrives, Tuppence confronts the fleeing Mrs. Vandemeyer alone. Mrs. Vandemeyer draws a gun, but Tuppence overpowers her and offers one hundred thousand pounds for Jane Finn's location, news of Tommy, and Mr. Brown's identity. Mrs. Vandemeyer agrees but faints from a heart condition when Sir James and Julius appear. They keep vigil through the night, yet in the morning she is found dead from an apparent chloral overdose. Sir James departs with a cryptic warning: "Never tell all you know, not even to the person you know best."

Dr. Hall, who runs a Bournemouth nursing home, confirms that Mrs. Vandemeyer placed a girl with complete amnesia in his care since 1915, claiming she was a niece traumatized by the Lusitania. The girl was removed the evening Julius visited the nursing home while trailing Whittington. Julius proposes to Tuppence; she refuses, realizing she loves Tommy.

The narrative backtracks to Tommy's captivity in the Soho house. He bluffs his captors into keeping him alive by claiming he can locate the Danvers papers. A young French servant named Annette brings him food. When his bluff is exposed and his captors tie him up, Annette secretly slips him a penknife. Tommy cuts his bonds, overpowers his guards, and escapes with her help. Annette refuses to leave, shouting three times, "I want to go back to Marguerite!" Tommy does not grasp the significance. Carter raids the house, but the gang has fled.

Tommy discovers Tuppence vanished after receiving a forged telegram directing her to Yorkshire. He and Julius rush there but find only her brooch. Sir James then announces Jane Finn has been found in Manchester: A girl recovering from a street accident claims she hid the treaty in a cliff near Holyhead. Tommy and Julius race there, but the packet contains only the message "WITH THE COMPLIMENTS OF MR. BROWN." The episode was a decoy. Back in London, Carter reveals that Tuppence's coat and hat have washed ashore in Yorkshire; she is presumed dead.

Tommy is devastated, but a crucial discovery follows. In Julius's sitting room, he finds a photograph of Annette in Julius's desk. This is the photograph of Jane Finn that "Inspector Brown" supposedly stole, proving it never left Julius's possession. Tommy's suspicion deepens when he recalls that a note forged in Tuppence's name, left as part of the deception surrounding her disappearance, was signed "Twopence." This misspelling could only come from someone who had never seen her nickname written down. Julius had seen it; Sir James had not.

Tommy writes to Carter, arguing that Tuppence's death was staged and the Manchester girl was a plant. He travels to Gatehouse, Kent, where the original telegram actually directed Tuppence. At Astley Priors, a private doctor's estate, he spots Tuppence in a window and signals her. Separately, Julius confronts Kramenin, the Russian revolutionary Tommy recognized as "Number One" from the Soho meeting, at gunpoint and forces him to reveal the girls' location. Julius drives to Kent and bluffs the captors into releasing Tuppence and Annette. Tommy leaps onto the escape car and sends Tuppence and Jane to Sir James in London, keeping Julius with him at gunpoint.

At Sir James's house, Jane Finn reveals her true identity. She is not French; she is the real Jane Finn, who faked amnesia and adopted a French persona for five years to survive captivity. On the Lusitania, suspicious of Mrs. Vandemeyer, she substituted blank sheets in the oilskin packet and hid the real treaty between the advertisement pages of a magazine. Captured before reaching London, she endured years of imprisonment. In the Soho house, she concealed the treaty behind the backing of a painting of Marguerite from Goethe's Faust. Her cries of "Marguerite!" during Tommy's escape were attempts to direct him to the painting.

Sir James insists they go to the Soho house. Jane recovers the treaty from behind the painting, and Sir James pockets it. He then reveals himself as Mr. Brown, planning to kill the girls and walk out with the document above suspicion. But Tommy and Julius, who raced to London and hid behind the upstairs curtain, seize him and wrench away his revolver. Cornered, Sir James raises a signet ring containing cyanide to his lips and dies.

With Mr. Brown dead, his organization collapses. The 29th passes without revolution. The Labour leaders accept government concessions, and the treaty is burned. Sir James's diary, later discovered, reveals a megalomaniac who used his brilliant legal career as a mask for criminal ambition. At a celebratory supper at the Savoy, Tommy explains his deductions, and his estranged uncle, Sir William Beresford, reconciles with him and names him his heir. Julius proposes to Jane, who accepts. Tommy and Tuppence finally confess their feelings and plan a future together.