Former lab chimp Bonzo, suddenly literate, runs away from a carnival sideshow. He lands in the college town of Pawlton, where young Betsy mistakenly believes the chimp is a gift from her grandfather, Pop Drew, the football coach at Pawlton.
Betsy wants to formally adopt Bonzo, something her parents, Marion and Malcolm Drew, aren't too sure about. A judge goes along with the idea, pretending to officially approve an adoption, just to humor the girl. Betsy then writes her other grandfather, millionaire Clarence Gateson, to inform him she now has a baby brother. Gateson is thrilled until he arrives in Pawlton and finds the truth.
Gateson warms up to Bonzo and even takes him golfing. Discovering what a natural athlete the chimp is, an idea is hatched that Bonzo could play quarterback for the college, where Pop is desperate for good players. A couple of con men, Edwards and Crane, kidnap the chimp just before the big game and replace Bonzo with one that can't play ball. Before they can collect their bets, the real Bonzo turns up and wins the game.
- Gigi Perreau as Betsy
- Edmund Gwenn as Pop
- Maureen O'Sullivan as Marion
- Charles Drake as Malcolm
- Gene Lockhart as Gateson
- Jerry Paris as Edwards
- John Miljan as Crane
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