The film follows musical composer George Webber (Dudley Moore) as he goes through a midlife crisis. Much to the chagrin of his actress girlfriend Samantha Taylor (Julie Andrews), George starts ogling younger women and conspicuously spies on his next-door neighbor who frequently hosts orgiastic parties.
Suddenly he spots an exotically beautiful young woman by the name of Jenny (Bo Derek), who's on her way to her wedding. George then makes it a goal of his to have an affair with her, even though she's newly married, and even if he has to follow her and her husband to Mexico on their honeymoon.
This film is Best Known for the Fanservice, as Bo's sexy one-piece swimsuit and cornrow-festooned hair made her a locker-room-poster sensation in the late seventies, dethroning the previous reigning pin-up queen Farrah Fawcett. But her career wasn't the only one boosted by it — for most audiences outside of the U.K., this was their introduction to Dudley Moore, who subsequently toplined a clutch of romantic comedies in the early 1980s.
This film contains examples of the following tropes:
- George, big time, who falls in love with Jenny behind his girlfriend's back.
- Jenny could also count, as at the end she has no problem in sleeping with George even though she's married. Subverted when after the act it's revealed that Jenny and her husband have an open relationship, much to George's dismay.
- Award-Bait Song: A lower-key but still award-baity Oscar nominee from 1979 was this film's theme "It's Easy to Say". It's a mellow, piano-based Silly Love Song with touching lyrics — but it's also important to the story, even though the film is not a musical, as it's the song used by George (a composer) to reconcile with his estranged girlfriend at the end of the film.
- Boléro Effect: Maurice Ravel's signature piece is, according to Jenny, the perfect music to make love to. In this case, the effect may well be the... um... climax.
- Dirty Old Man: George, no doubt. He's in his forties, but has no problem going after Jenny, who going by her actress's actual age at the time, is in her early twenties.
- Distracted by the Sexy: George is so distracted when a car bearing Jenny drives by that he drives right into another car. A police car.
- Gave Up Too Soon: At the end of the movie, George's neighbor spies with a telescope on George and Samantha talking. He angrily says he's tired of always giving George a show and getting nothing in return and goes to bed. Almost as soon as he does, George and Samantha reconcile and start having sex.
- Genre Deconstruction: George learns his fantasy girl is exactly that. Jenny isn't a bad person but George is sorely disappointed to realize that he threw away a relationship with a decent and loving woman for someone who only sees him as "a casual lay", as she puts it.
- Lucky Charms Title: Officially, the quotation marks around "10" are part of the film title.
- Ms. Fanservice: Take a wild guess.
- One-Word Title: Also a Title by Number.
- A Party, Also Known as an Orgy: Takes place on a regular basis next door to George's house.
- The Peeping Tom: George and his next door neighbor with their telescopes. They know they're spying on each other to boot.
- Polyamory: Jenny and David have an open relationship, as George eventually learns to his dismay.
- Pretty Fly for a White Guy: Jenny's cornrows had been a popular hairstyle for black people throughout most of the seventies.
- Pyrrhic Victory: George gets to hook up with Jenny, but he's not too thrilled about it anymore once he learns Jenny and David are in an open marriage.
- Stalker with a Crush: George, as soon as he meets Jenny. This is a bit of Values Dissonance, as this wasn't taken nearly as seriously at the time.
- Title by Number: Also a One-Word Title.
- Vanity License Plate: Samantha's license plate reads "SAM 1". George's license plate reads "ASCAP". This acronym stands for the "American Society of Composers, Authors, and Publishers" - the guild for songwriters, which is appropriate since George is a composer.