A naive young man is sent to Washington to fill in for an ailing senator, but once in the Capitol, he meets so much corruption that he is compelled to denounce it.

Jefferson Smith is a small town idealist who answers the call to duty when he's unexpectedly named to fill a vacant seat in the U.S. Senate. Determined to do some good, he sponsors a bill to create a national boy's camp, unaware it threatens to undermine a graft scheme sponsored by his home state's crooked political machine. Framed and threatened with expulsion, Jefferson takes to the Senate floor to prove his innocence.