This movie had me pretty much from the moment when a priest in an Indian temple spots an approaching party and yells "Tourists!" at which point everybody puts on a show of peasant-y exoticism for the visiting rubes.
One of those rubes is Marmaduke Paradine (David Hutcheson) who is a rake and a scoundrel, and while visiting the temple takes the rakish and scoundrel-ish step of stealing an eye from the idol in the temple. Suspecting that this might not have been the best idea, he palms the eye off on his more upright cousin Paul Bultitude (Roger Livesey) when he returns to England. What Paul and his son Dick (Anthony Newley) don't realize is that the eye has magic powers; when each of them express the wish that they could live the other's life, it's granted. Which means that stuffy Paul is suddenly a giddy 12-year old, eating ice cream, trying to kiss the pretty parlormaid (Patricia Raine) and generally having a wonderful time. Meanwhile, Dick returns to boarding school a tired, annoyed middle-aged man, which causes no end of unhappiness for Dulcie Grimstone (Petula Clark), the headmaster's daughter and once the apple of Dick's eye . . .
The film was written and directed by Peter Ustinov, working from the comic fantasy by F. Anstey, and if nothing else, this is one of the few British films that has no love for the "public" schools that are so often portrayed as heaven on earth and the builders of the perfect Briton. Ustinov, whose own years at a prep school were quite miserable, sees the places as holding pens for bored, lonely, unhappy kids, who take their frustrations out on each other. And also as ideal stalking grounds for adults with, well, issues. (James Robertson Justice plays brilliantly against his usual beardy, bellow-y type as the headmaster, Dr. Grimstone, a man who enjoys spanking WAY too much.) Fortunately, there's a lot more. For one thing, there's Roger Livesey's performance as Paul, which is playful and sweet without going over the top (Livesey was flat-out one of the most likable actors to ever work in films). And Anthony Newley, despite his wide eyes and un-broken voice, does middle-aged sourness and stuffy disapproval quite convincingly. Your despair for him is increased by the fact that his personality change loses him the affections of Petula Clark, whose film career did NOT begin with FINIAN'S RAINBOW, and who demonstrates she was just as dab a hand at acting as she was at the whole singing thing. I've mentioned James Robertson Justice already, so one should also give a shout out to David Hutcheson as the snake who sets everything in motion and Kay Walsh as his girlfriend, who almost tricks the personality-switched Paul into marrying her, the better to con him out of his money.
Ustinov doesn't dazzle as a "new" directorial talent the way, say, Orson Welles did, but the film bursts with mischief and high spirits the way that nothing else that Ustinov did as a director ever did. Which is a pity. Oh well, be glad for what you get.