Passenger to Frankfurt is a 1970 novel by Agatha Christie.
It's not a murder mystery like most of Christie's works, but rather a spy thriller—in fact, the last of the spy thrillers that she'd written from time to time since the 1920s. Sir Stafford Nye is a rather undistinguished mid-level diplomat. While waiting in the Frankfurt airport he meets a mysterious young woman who asks him for his passport. She will board his plane while pretending to be him. She begs him for help because, if he doesn't help her escape, she will be killed. Sir Stafford, intrigued, agrees to help, and lets her take his passport, which he reports as stolen.
Nye eventually gets back home where he's quizzed by his acquaintances at the Foreign Office. It turns out that the woman who took his passport is a spy code named "Mary Ann". Nye, intrigued, puts out a subtly coded message for her in the newspaper. The woman makes contact with him and invites him to an opera. The woman, whose real name is Countess Renata Zerkowski, eventually enlists Nye's help in exposing a secret conspiracy. The conspiracy, aimed at nothing less than taking over the world, seeks to manipulate left-wing student protest movements into the establishment of a Nazi Fourth Reich.
- Added Alliterative Appeal: Sir Stafford says that the Nazi youth movement is engaging in "high explosives, hijackers, high jinks."
- Argentina Is Nazi-Land: It turns out that Adolf Hitler changed places with a double in 1945 and eventually escaped to Argentina. He went crazy and died after a while, but the Nazi conspiracy of the 1970s is passing off a young man as his son.
- Author Tract: Agatha Christie, an 80-year-old rich English lady, was obviously terrified by the student youth movement and protests like the May 1968 uprising in France. In this story those protests are the harbinger of a world uprising of gullible young people being manipulated through sex and drugs by a neo-Nazi movement.
- Brainwashing for the Greater Good: At the end this has become the case. In order to counteract the mass uprising of indoctrinated young people actually working for a neo-Nazi group, a chemical that basically removes any trace of aggression or ill-intent towards another human being is massively released. This is treated as an unadulterated happy ending.
- Chekhov's Gunman: Milly Jean Cortman, wife of the American ambassador in Britain, whom Sir Stafford meets at an embassy party that he attends with Renata. Milly Jean is eventually revealed to be "Juanita", the assassin in league with the Nazis (she kills her own husband).
- Conspiracy Thriller: The British government trying to destroy a secret society bent on taking over the world and establishing a new Nazi state.
- Fat Bastard: Countess Charlotte von Waldsausen, one of the leaders of the neo-Nazi movement, is morbidly obese.
- Fourth Reich: The Countess von Waldsausen is orchestrating a worldwide movement to use student youth to bring the Nazis back into power, with her front man being a young fellow from Argentina who is supposedly Hitler's son (although it turns out to be a hoax).
- I Was Quite a Looker: Sir Stafford's Aunt Matilda says offhand that "I wasn't bad looking when I was young."
- Leaning on the Fourth Wall: As the mystery lady is asking Sir Stafford for his passport so she can escape assassins, he snarks, "You know what you're talking like? A beautiful spy in a thriller."
- Meet Cute: A spy version of Meet Cute as Renata comes up to Sir Stafford in an airport, and says that she has to have his passport to escape assassins that are waiting for her.
- The Mole: James Kleek is revealed at the climax to be a mole in league with "Juanita" and the neo-Nazi conspiracy. He tries to murder Lord Altamont.
- Napoleon Delusion: A creepy German psychiatrist tells the good guys that he ran a hospital with a whole ward of people who imagined that they were Napoleon, or Hitler, or Julius Caesar. It seems that in the last days of the war one of the Hitler nutcases was switched out with the actual Adolf Hitler, who made his escape to South America.
- Next Sunday A.D.: Set at some vague future date where student protests like May '68 have continued to spiral out of hand, with Washington DC having been burned to the ground, civil unrest everywhere, most European airports destroyed, and the like.
- No Celebrities Were Harmed: The unnamed French Marshal is a clear reference to Charles de Gaulle. (In Real Life De Gaulle died just a couple of months after this book was published.)
- Old Retainer: Sir Stafford's Aunt Matilda is attended by a fellow named Horace, who was once a groom, once a coachman, now a chauffeur, and is still working for Aunt Matilda at age eighty.
- Spell My Name with a Blank: Dr. Reichardt tells how in the closing days of the war Adolf Hitler himself visited the asylum in the company of his aide, one "Martin B."—Bormann, that is.
- Title Drop Chapter: The first chapter, in which Sir Stafford meets the mystery lady in the airport, is titled "Passenger to Frankfurt".
- Trust Password:
- Sir Stafford, when he is approached by some Brits in league with the Nazi conspiracy, shows that he is one of them (or rather, pretends that he is one of them) by pulling out a recorder and playing a snatch from Wagner's opera Siegfried.
- And immediately after that, when he gets a phone call from the Foreign Office, he answers the question "Sir Stafford?" with the code phrase "No smoke without fire."
- The 'Verse: Mr. Robinson, a shadowy figure who is said to know international finance quite well, and is on the side of the good guys trying to thwart the conspiracy. This character appeared before in Christie novels Cat Among the Pigeons and At Bertram's Hotel (and would appear again in the last novel Christie ever wrote, Postern Of Fate).