A young congressman tries to rid Washington of corruption while courting a senator's daughter.

Onboard the Congressional Express, a train bound for Washington, D.C., is the Honorable Button Gwinnett Brown, a newly elected member of the United States House of Representatives. Button looks at an original letter from his ancestor, Button Gwinnett, one of the signers of the Declaration of Independence, but the letter blows into the compartment of Alice Wylie, the granddaughter of an influential senator, who promptly tears it up as trash. Button is dismayed because the document was one of only three surviving letters written by his namesake. Meanwhile, Carl Tilden, head of the prohibition department, visits bootlegger Edward T. Norton. Tilden threatens to expose Norton and resign, but Norton reminds Tilden of his power and adds that Tilden can expect a term in Leavenworth. Tilden leaves and writes a letter to his friend Button, then kills himself. When Button arrives at the depot, he is met by Willis, who has been appointed as his secretary by the local boss, Kelleher, an associate of Norton. Willis carries a telegram that orders Button to vote for a bill that would ensure a permanent place for the relics of General Digger, but Button, intent on political integrity, rejects Willis' proposal. On the steps of the Capitol, Button meets his old pal Pete, and together they visit the Bonus Army. Button lectures the group on political corruption and explains that he has learned that he was elected with stolen votes and now plans to double-cross the crooks who put him there. Button returns to his apartment and, after putting Kelleher in his place, reads Tilden's letter. Button then goes to the Library of Congress to research the Digger bill and discovers that it is a fraudulent bill meant to honor a man who stole land from the native American Indians. Button meets with Alice, who after agreeing to work for him, tells him that Kelleher is having the ballots recounted to recall Button from office. On the floor of the House, Button exposes the Digger bill. After being removed from office, Button is counseled by Alice's grandfather, Senator Wylie, whom Button accuses of being controlled by Norton. At first denying Buttons' allegations, Wylie soon recognizes that Button is right, but before he can mount an investigation, he is poisoned by his chief aide, Martin, a Norton spy. At Wylie's funeral, Alice is accompanied by Norton, who proposes marriage and outlines his plan to gain control of the nation's newspapers and political machines. Button exposes Norton's scheme to the Bonus Army, and they capture Norton, who is charged with the murder of Tilden, Wylie and the United States Marines who were killed in Latin America while defending his crooked financial interests. Norton futilely attempts to bribe Button, who leaves Norton a gun, with which he kills himself. As they leave, Alice asks Button to put his arm around her.