A man...a statesman...is to be killed...assassinated...in London...soon...very soon. Tell them...in London... Ambrose Chappell...
The Man Who Knew Too Much was first a 1922 book of detective stories, then a 1934 film by Alfred Hitchcock, who remade the film in 1956.
The 1934 film: featured Peter Lorre as a villain; with Leslie Banks and Edna Best as Bob and Jill Lawrence as a British couple who find themselves having to help stop an assassination.
In the 1956 film: James Stewart and Doris Day star as Ben and Jo McKenna, Americans traveling to Morocco with their son Hank (Christopher Olsen). On the bus they meet the amiable Bernard, who puts Jo on edge for remaining mysterious while asking them numerous questions about themselves. Soon her suspicions are confirmed when Bernard stumbles out of a crowd, in disguise and mortally wounded, to whisper a secret message to Ben with his dying breath. Unwittingly embroiled in events beyond their understanding, Ben and Jo quickly learn that there are dangerous people out there who very much want to keep the information a secret.
Adult Fear: The heroes try to thwart the assassination plot mainly because the assassins kidnap their child, Betty, and threaten to destroy her if they give the police the information that Bernard left.
Chekhov's Gun: Many of the elements appearing in the first two scenes become significant later on.
Jill's shooting ability comes in handy when rescuing her daughter at the end.
Ramon's shooting, demonstrated in the same scene, becomes part of the assassination plot.
Abbott's musical watch alerts us to his presence when he reappears.
Jill gives Betty a brooch. The brooch is later given back to Jill as a reminder that the bad guys still have Betty prisoner.
Adapted Out: The mother's brother, who helped search for the assassins' base in the '30s movie.
Adult Fear: The heroes try to thwart the assassination plot mainly because the assassins kidnap their child, Hank, and threaten to destroy him if they give the police the information that Bernard left.
Artistic Title: An orchestra performs the main title against the opening credits to establish the importance of music in the plot.
Becoming the Mask: Mrs. Drayton, who pretended to be nice to Hank, only to try and save the him near the films climax.
Bilingual Bonus: Bernard speeks Arabic and French unsubtitled at different moments.
Black Comedy: Ben's and Jo's conversation about how as a doctor, people must suffer in order for Ben to make enough money for vacations.
Break the Cutie: Jo has a Heroic BSOD after Ben tells her about Hank's kidnapping not only out of Adult Fear, but also out of anger for Ben tricking her into swallowing a sedative beforehand, as an attempt to keep her nerves calm.
Look at her face during the Albert Hall sequence, and you can see a woman who's about to lose it, who knows that something terrible is about to happen and cannot do a thing about it...until she just snaps and screams.
Near the climax, she hears Hank whistle to "Qué Será, Será" while she plays on the piano. Becuase she knows he's nearby, but can't do anything to help him, except play.
Breaking the Fourth Wall: Jimmy Stewart hosted the trailer as himself, telling the viewers of different places he visited for Hitchcock's then-upcoming movie. The ad also dubbed over a clip so that one of the characters would refer to Jo as Doris Day.
Brick Joke: In the second act, Ben and Jo excuse themselves from some guests, claiming that they have to pick up Hank from his babysitters. In the epilogue, they return to the apartment a full day later to find the guests are still there, asleep, and apologize for taking so long.
Bernard just happens to stumble into Ben on a crowded street just before dying. The police point out how unlikely that is.
It's also convenient that by the time Jo tries to call the Scotland Yard inspector to help save Ben from the kidnappers, he has left for Albert Hall. When Ben and Jo go there to see him, all three of them end up at the site of the assassination attempt.
Mistaken for Spies: Bernard mistakes Ben and Jo for the spy couple that he's looking for. The Moroccan police also find it very suspicious that Bernard just happened to stumble into Ben and Jo on a crowded street just before dying.
Police Are Useless: The Moroccan police are suspicious and unhelpful. When Jo calls the London police saying that they've cornered the kidnappers and her husband is in danger, the head officer is away and his subordinate seems uninterested in helping. He's eventually convinced to send a single squad car, who don't do anything but knock on the door.
Red Herring: Ambrose Chappell the taxidermist has nothing to do with the assassination plan, or the kidnapping.
Sequel Escalation: Considering the two of them share the same director and largely the same plot, many viewers will be surprised how more down-to-Earth the original was compared to the epic scale of the 1956 remake.
That Reminds Me of a Song: Used as a plot device. Doris Day sings "Qué Será, Será" multiple times, ultimately using it in a game of Marco Polo so our heroes can find their kidnapped offspring.
Women Are Wiser: Played straight many times. Jo becomes Properly Paranoid of Louis and the Draytons earlier than Ben does, and later throws off the aim of the Prime Minister's assassin. Ben plays a larger role than she does in Hank's rescue, though.