The Secret Adversary is a 1922 detective fiction novel by British writer Agatha Christie, introducing the characters of Tommy and Tuppence, two Young Bright Things in The Roaring '20s.
The novel starts with a Prologue, during the sinking of RMS Lusitania in May 1915. A mysterious man approaches a young American woman, trusting her with important papers as she is more likely to survive.
Four years later in London, demobilised soldier Tommy Beresford meets war volunteer Prudence "Tuppence" Cowley. They are both penniless and resolve to become adventurers, forming "The Young Adventurers, Ltd". Tuppence hears two men talking about a "Jane Finn" woman, before she is approached by one of the two gentlemen, Mr Whittington, who offers Tuppence a suspiciously comfortable job (posing as a young American woman in a French college). When Tuppence suggests she uses the alias "Jane Finn", Whittington turns paranoid. He gives her £50 and then disappears. Curious, they advertise for information regarding Jane Finn.
The advertisement yields two replies. The first is Mr Carter, a British intelligence leader Tommy met during his war service. Carter informs them Jane Finn, who was aboard the Lusitania when it sank, received a secret treaty to deliver to the American embassy in London. She was listed among the survivors but she has disappeared after the ordeal. However the treaty she held must be found, as if its existence was made public, it would compromise the British government. They agree to work for him, despite his warnings of the eponymous secret adversary, the dangerous Mr. Brown, a seemingly random guy who is actually the mastermind of a dangerous agitator organisation. Mr. Brown was in the next room when Tuppence was received by Whittington.
The second reply comes from Julius P. Hersheimmer, an American multimillionaire and cousin of Jane Finn, intent on finding her as he's her only living relative and wants to share his inheritance with her. Mr. Brown has already conned Julius into giving him the only existing photograph of Jane, posing as a Scotland Yard agent. Tommy and Tuppence join forces with Julius to investigate about Jane's disappearance and uncover Mr. Brown's organisation.
The novels displays the following tropes:
- Amoral Attorney: Sir James is a King's Counsel (a senior trial lawyer) and refers to his defending criminals in court as "taking care of one's own people".
- Beneath Notice: Mr. Brown, the mastermind of The Secret Adversary, often appears in menial positions and lets others in his organization stand out while he slips in orders in secret. Tuppence actually sees him, posing as a secretary at Esthonia Glassworks that passes a phone message on to Whittington, and she remembers absolutely nothing notable about him. She even meets him again later in another guise and completely fails to recognise him.
- Better to Die than Be Killed: Mr. Brown a.k.a. Sir James knows he will get no leniency from the government for his schemes. He takes a cyanide pill hidden in his signet ring.
- Bluff the Eavesdropper: Jane wails in French to convince her kidnappers she's really lost her memory.
- Childhood Friend Romance: Part of the arc is Tommy and Tuppence confronting their feelings for each other.
- Les Collaborateurs: Mr. Brown's organization are dangerous agitators.
- Cyanide Pill: Sir James would rather die than be caught and tried as Mr. Brown. He keeps one hidden in his signet ring.
- Damsel in Distress: Jane Finn is both this and a Living MacGuffin.
- Distressed Dude: Tommy is caught by the bad guys.
- Detective Mole: The main characters are trying to locate the treaty and keep it from falling into the clutches of Mr. Brown. Sir James Peel Edgerton KC is himself Mr. Brown, and is using their efforts to find the treaty.
- Dirty Communists: The bad guys who will ruin Britain with the missing document in The Secret Adversary. That being said, they appear to be merely a means to an end, manipulated by Mr. Brown. Also appears to a lesser extent in Partners in Crime.
- Fake American: In-universe, Tuppence pretends to be a heavily-accented American secret agent to get information from Albert. He's amazed at how natural her accent sounds when she later comes back in disguise, "pretending" to be British.
- Forged Message:
- Tuppence receives a telegram from Tommy asking her to meet him urgently. Shortly afterward, it is revealed that Tommy never sent any telegram and Tuppence has been taken hostage by the villains.
- Later, the villains attempt to mislead Tommy with a false message from Tuppence, but the author of the message makes an error that allows Tommy to realise it's a fake.
- Hollywood Spelling: A forger incorrectly signs Tuppence's name as "Twopence" on a note and gives Tommy the final clue he needs to solve the mystery.
- I Call It "Vera": Julius carries a pistol he calls "Little William".
- Kissing Cousins: Julius falls in love with his cousin Jane from afar, which is one of the reasons he's so desperate to find her. He does, and lucky for him, she returns the affection.
- Love at First Sight: Julius. From a mere picture of Jane.
- MacGuffin: The draft of a treaty, drawn up During the War. The reader never learns what it says, only that its revelation would be disastrous for the British Government. When it is found near the end of the book, Mr. Carter promptly burns it.
- The Man Behind the Man: Mr. Brown for Whittington, and later Boris.
- Marriage of Convenience: With the possibility of both Tommy and Jane being gone for good, Julius asks Tuppence to marry him out of concern and respect for her, trying to lure her in with the promise of his riches. She turns him down, since she still feels strongly for Tommy.
- Men Are the Expendable Gender: Danvers gives Jane Finn the papers when the Lusitania is torpedoed, saying that she has a better chance of making it off the ship than he does.
- Merciful Minion: Annette, who is the only person in the safehouse who doesn't want Tommy dead.
- The Mob Boss Is Scarier: Rita Vandemeyer is terrified that Mr. Brown will get to her, even after Julius and Sir James assure her that she will be quite safe with them. After she is found poisoned, it is suspected that she killed herself rather than betray Mr. Brown, because they see no way anybody else could have come into her flat during the night. Sir James poisoned her, as he is Mr. Brown, because she was considering Julius' bribe to tell what she knew.
- Mr. Smith: The mysterious Big Bad is known only as "Mr. Brown".
- Similarly, Tommy's contact in British Intelligence calls himself "Mr. Carter" but it is made clear that is not his actual name.
- Poison Ring: Sir James has one, and uses it after he gets caught as Mr. Brown.
- Smart People Know Latin: Sir James knows it quite well. Enough that his dying words after taking cyanide are "'Ave, Caesar! te morituri salutant!" note
- Spotting the Thread: Tommy recognises a letter from Tuppence is a fake because it is signed "Twopence". The villain had only ever heard her nickname spoken and didn't know which spelling she used.
- Trauma-Induced Amnesia: Annette, according to Dr. Hall. Subverted; she was bluffing the entire time.
- Two Aliases, One Character:
- The search for Jane Finn is hampered by the fact that none of the heroes have any idea what she looks like; the man who entrusted her with the macguffin died before passing on a description, and there's only one known photograph of her, which is in the hands of the enemy. When Tommy gets hold of the photograph near the end of the novel, he realises that he's already met Jane Finn, who was pretending to be a French woman named Annette.
- When Mr. Brown is unmasked at the end, it's revealed that he's a character who was introduced separately and has previously interacted with the heroes on several occasions.
- Unspoken Plan Guarantee: Tommy's ultimately successful plan to unmask Mr. Brown and recover the vital document is kept from the audience and the other characters until he successfully pulls it off. Justified by the fact that he doesn't want to let slip any information that might be learned by Mr. Brown except for the information he deliberately lets out to fool Mr. Brown.
- Wealthy Philanthropist: Julius, the generous millionaire benefactor, who not only insists on paying for everything for Tommy and Tuppence while they help him try to find his missing cousin, but even offers to help himself like a true Nice Guy.
