"John Smith" (Colman), an amnesiac soldier in the First World War, wanders away from the asylum he is confined to when the gatekeepers abandon their posts to join a party celebrating the end of the war. He meets Paula (Garson), a singer, and they leave the town and go to a village in Devon where they marry and have a son. Then he goes to Liverpool for a job interview, is hit by a car, and comes to with his original memories restored, but his memories of his life with Paula forgotten...
Random Harvest provides examples of:
- Accidental Adultery: The main character is an amnesiac who, oblivious to the fact that he is already married, becomes engaged to a young admirer. His wife has tracked him down and attempted to trigger his memories of her, but failed; before this trope can take full effect, his wife has his alter ego declared dead and their marriage annulled, after which his new fiancée breaks off the engagement anyway.
- All Love Is Unrequited / Love Dodecahedron: Oh boy... Kitty loves Charles, who thinks he loves her but is still in love with his wife, who he's forgotten all about, Paula is still in love with John/Charles, a psychiatrist who used to know John is in love with Paula, Charles marries Paula without knowing she's already his wife, and she finds it hard to love him because he's not John anymore...
- Amnesiac Hero: John Smith/Charles Rainier. Unlike most examples, he can't remember his own name, and when he regains his original memories, he can't remember his other name.
- Amnesiac Lover: John/Charles can't remember who Paula is, even when she comes to work for him. She doesn't tell him who she really is, though.
- Brief Accent Imitation: Paula does this in her vaudeville act where she sings in a Scottish accent.
- Death of a Child: John and Paula's son, who dies after John regains his memories.
- Easy Amnesia: John Smith loses his memory in the trenches, then regains it in a car accident.
- While this trope is played mostly straight, it is averted in one respect. While most Easy Amnesia cases are people who have lost their memories but are otherwise fully functional, "John" seems to have forgotten how to talk, and has to re-learn.
- Edgy Backwards Chair-Sitting: A rare female example and all the more interesting since Paula does this while in her very short kilt.
- Girl Friday: Halfway through the movie it's revealed that Paula is working for Charles. She saw his picture in a magazine, and looked him up. When he didn't remember her, she took a job as his executive assistant.
- I Want My Beloved to Be Happy: Kitty, when she realises John/Charles is still in love with someone else (even though he doesn't know he is).
- The Jailbait Wait: Charles' 15-year-old step-niece Kitty says straight-up that she wants to marry him and asks him not to do "anything rash" over the next three years until she becomes legal.
- MayDecember Romance: Between Kitty and Charles.
- The Reveal: Paula has been working as John/Charles' secretary under the pseudonym of Margaret for several years. Constantly seeing her has made no difference to his memory, unfortunately.
- Saying Too Much: A heroic version. While back in the town he met Paula in, Charles makes a comment to his friend about a shop he can get cigarettes in. The friend promptly points out that since he's never been there before, he shouldn't know that. Cue Charles slowly regaining his memories.
- She's Got Legs: Paula does her Music Hall number in the shortest skirt you'll ever find in a 1940s film.
- Spared by the Adaptation: In the book, Kitty dies. In the film, she goes travelling.