In the middle of the Great Depression, Longfellow Deeds , co-owner of a tallow works, part-time greeting card poet and tuba-playing inhabitant of the hamlet of Mandrake Falls, Vermont, inherits the enormous fortune of 20 million dollars from his late uncle, Martin Semple. His uncle's scheming attorney, John Cedar , locates Deeds and takes him to New York City.

Cedar gives his cynical troubleshooter, ex-newspaperman Cornelius Cobb , the task of keeping reporters away from the heir. He is outfoxed, however, by star reporter Louise "Babe" Bennett , who appeals to Deeds' romantic fantasy of rescuing a damsel in distress by masquerading as a poor worker named Mary Dawson. She pretends to faint from hunger in his presence and worms her way into his confidence. She proceeds to write a series of enormously popular articles mocking Longfellow's hick ways and odd behavior, naming him the "Cinderella Man". Meanwhile, Cedar tries to get Deeds' power of attorney in order to hide his financial misdeeds.

Deeds, however, proves to be a shrewd judge of character, easily fending off Cedar and other greedy opportunists. He wins Cobb's wholehearted respect and eventually Babe's love. However, when Cobb finds out Bennett's true identity, Deeds is left heartbroken...

...Alarmed at the prospect of losing control of the fortune, Cedar joins forces with Deeds' only other relative and his grasping, domineering wife in seeking to have Deeds declared mentally incompetent. This, along with Babe's betrayal, finally breaks his spirit and he sinks into a deep depression.

excerpted form wikipedia