British school kids Will and Lee are both about 11 years old, but they don't have much in common. Will is a sheltered lad whose religious upbringing forbids TV-watching and all sorts of other sinful stuff. Lee is a little hellion, constantly in trouble.
One day Lee gets Will in trouble, and when they're sent together to the principal's office, he takes advantage of Will's relative inexperience by offering to take the blame — and the torture, which he describes in some detail — if Will gives him something in return. Will gives up both his dad's wristwatch and a promise: to be stuntman in Lee's secret project, an amateur version of Sylvester Stallone's Rambo: First Blood that he's making with a videocam swiped from his brother.
Now, Rambo is quite an introduction to movies for a kid who's never seen one, and Will is devout enough to find the whole notion guilt-inducing ... for about three seconds, after which he's smearing himself with dirt and leaping from trees with wild abandon, calling himself Son of Rambow. (Spelling is neither boy's strong suit.)
And thus a sequel is born. It grows bigger when Will spills the beans: Suddenly half the school wants in on the action. (Among the joiners is a French exchange student who, with his pointy red boots and his bleach-blond forelock, may be the world's least likely ninja warrior.) As the little movie that could acquires sets, costumes and a cast of maybe a dozen, young Lee, whose dream it originally was, loses control — of the project and of his temper.
If Tom Sawyer and Huck Finn had had access to a camcorder, the adventures in this movie-besotted movie might be the sort of thing they'd have dreamed up. Writer/director Garth Jennings sets the film in the 1980s, a time when, as it happens, he was about 11 himself. He's given the story some texture with non-cinema-related stuff — about bullying, childhood insecurity, religious family pressures and a loss of innocence. Mostly though, he's made the Son of Rambow film you're seeing feel a lot like the Son of Rambow film-within-a-film that the kids are making — cheerfully ramshackle, childishly overstated and pretty darn appealing.