Tommy and Tuppence

Tommy and Tuppence Beresford are the protagonists of a series of novels and short stories by Agatha Christie, and mark the few ventures that Christie made into espionage tales rather than the whodunits she's known for. They're far less famous than their mystery-solving counterparts Hercule Poirot and Miss Marple.

Appearing in Christie's second novel, The Secret Adversary, Thomas Beresford and Prudence "Tuppence" Cowley started out as friends in post-World War I Britain. Jobless and penniless, they place an ad in the paper marketing themselves as adventurers, leading to an encounter that starts their career as spies for an unnamed British intelligence agency. From there, they were revisited by Christie from time to time, and again, unlike Poirot and Marple, aged in real-time as Christie did, starting out as energetic twenty-somethings in The Secret Adversary and ending up as retired grandparents in their twilight years in Postern of Fate. Postern is also notable as the final novel Christie ever wrote, though not published.

Interestingly, the dedications of two Tommy and Tuppence books (The Secret Adversary and By the Pricking of My Thumbs) are the only times Christie ever dedicated a book directly to her readers.

The Tommy and Tuppence books are:

The Secret Adversary (1922)
Partners in Crime (short story collection) (1929)
N or M? (1941)
By the Pricking of My Thumbs (1968)
Postern of Fate (1973)

There was a live-action adaptation revolving around Tommy and Tuppence produced by London Weekend Television in 1983 of The Secret Adversary and several stories from Partners in Crime. The series was released in the United States as part of the PBS anthology series Mystery! Other various live-action adaptions have been done as part of other Agatha Christie-based series such as Marple.

The following tropes are common to many or all entries in the Tommy and Tuppence franchise.
For tropes specific to individual installments, visit their respective work pages.

Americans Are Cowboys: Some Conversational Troping between Tommy and Tuppence in Partners in Crime, where Tuppence wants to meet a handsome and rugged American man who can survive in the wild and rope a steer. Tommy asks her if he also wears chaps and a ten-gallon hat.
Almost-Dead Guy: Referenced at the beginning of Partners in Crime, when Tuppence wishes one would stagger through the door so she could have a mystery to solve.
Babies Ever After: After Partners In Crime. And again after they adopt Betty following the events of N or M?
Blackmail Is Such an Ugly Word: Tuppence improvises something similar to this to get money from Whittington in The Secret Adversary.
Bluff the Eavesdropper: Jane wails in French to convince her kidnappers she's really lost her memory in The Secret Adversary.
The Book Cipher: Tuppence finds one that starts the mystery off in Postern of Fate.
Book Ends: After creating Tommy and Tuppence, Christie would periodically go back and visit them from time to time. Rather sweetly, The Secret Adversary was the second published novel of Christie's career, and Postern of Fate was the third-to-last.
Bumbling Sidekick: Albert in The Secret Adversary. He improves over the course of the series, though.
Canon Welding: By The Pricking of My Thumbs and Postern of Fate both feature characters who have also appeared with Hercule Poirot and Miss Marple, despite Partners In Crime referring to Poirot as a fictional character.
Cold Sniper: Averted; Mrs. Sprot breaks down after she desperately shoots her daughter's kidnapper. Played straight, as it is later revealed she was acting to hide her cover.
Cover Identity Anomaly: Averted with Tommy and Tuppence in N or M?, although they both go about it in different fashions.
Cyanide Pill: Sir James would rather die than be caught as Mr. Brown at the end of The Secret Adversary.
Deadpan Snarker: Tommy.
Dirty Communists: The bad guys who will ruin Britain with the missing document in The Secret Adversary. Also appears to a lesser extent in Partners in Crime.
Disability Superpower: Tommy seems to have developed these in "Blindman's Buff". He later reveals his shades are fake and he was playing a joke on Tuppence.
Damsel in Distress / Dude in Distress: Tommy and Tuppence are both regularly caught by the bad guys. Occasionally veers into Badass Damsel with Tommy, especially with his escape in The Secret Adversary.
Genteel Interbellum Setting: The period of the first two books, The Secret Adversary and Partners in Crime.
Girl Friday: Tuppence plays one in most of the stories in Partners in Crime.
Grow Old with Me: Tommy and Tuppence aged in real time, unlike Christie's other detectives. By Postern of Fate, they were adventure-seeking grandparents.
The Handler: Mr. Carter in The Secret Adversary and Partners in Crime, and his replacement in N or M?
He Knows Too Much: The dead agent in N or M. Also used in The Secret Adversary with Tommy, but played with in that he only bluffs his way into the hideout and doesn't actually know anything.
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 in The Secret Adversary.
In Harm's Way: The whole point of the Young Adventurers, Ltd. in The Secret Adversary.
Ironic Name: Tuppence's real first name is Prudence; as the author notes, she rarely acts with any.
The Jeeves: Albert, starting in Partners in Crime.
Kissing Cousins: Julius and Jane in The Secret Adversary.
Les Collaborateurs: Mr. Brown's organization in The Secret Adversary.
Loose Lips: Tuppence pretends to have them to try and lure out the moles in N or M?
"London, England" Syndrome: Knowing the correct location of Maldon is a plot point in Partners in Crime.
Love At First Sight: Julius in The Secret Adversary. From a mere picture of Jane.
Magnificent Bastard: Mr. Brown in The Secret Adversary. Sir James had everyone fooled.
The Man Behind the Man: Mr. Brown for Whittington, and later Boris.
Masquerade Ball: The revolving point of the mystery in "Finessing the King/The Gentleman Dressed in Newspaper."
Master of Disguise: Tuppence disguises herself on a couple of occasions and manages to fool the right people.
Merciful Minion: Annette in The Secret Adversary.
The Mole: The whole point of N or M?
Mr. Smith: Mr. Brown in The Secret Adversary.
National Stereotypes: Used extensively, especially in The Secret Adversary, Partners in Crime, and N or M?
Only Known by Their Nickname: Tuppence.
Public Domain: The first book, The Secret Adversary, is public domain in the United States, and is available on Project Gutenberg.
Reading the Enemy's Mail: Tommy and Tuppence do this to the letters received by the International Detective Agency in Partners in Crime. And Tuppence uses fake letters her fake sons have written her to try and lure out the mole in N or M?
Red Oni, Blue Oni: Tuppence is red, Tommy is blue.
Red Scare: In both The Secret Adversary and Partners in Crime.
Sherlock Scan: Tommy attempts these a couple of times in Partners in Crime. Subverted, because the first time he guesses completely wrong, and the second time he was secretly eavesdropping on the man he was about to meet.
Shout-Out: Pretty much the entire point of Partners in Crime. All of the stories are Homages, and occasionally Parody Episodes, of several well-known classic detectives and popular mystery writers of the day. Christie doesn't even spare herself, as the last chapter extensively references Hercule Poirot!
Smithical Marriage: Tommy and Tuppence occasionally use aliases to protect themselves. The debate of which alias on one occasion in front of the hotel clerk leaves him aghast at the openness of their discussion; he doesn't realize they're married to each other!
Spoiled Sweet Julius, the generous millionaire benefactor of The Secret Adversary.
Spotting the Thread: Almost literally. Tuppence slips up on her cover in N or M? when she accidentally reveals she's quite good at knitting.
Spy Couple: Pretty much the whole point of the series.
Spy From Weights and Measures: The agency Tommy and Tuppence work for is never specified, but seems to go along these lines.
Sword Cane: Tommy carries one in "Blindman's Buff".
Trauma-Induced Amnesia: Annette, according to Dr. Hall in The Secret Adversary. Subverted; she was bluffing the entire time.
Unfortunate Names: Jane Finn, the oddness of which sets off the entire chain of events of The Secret Adversary.
We Do Not Know Each Other: Tommy and Tuppence while undercover in N or M?