It is a period of great recessions in the US, and the land is full of people who fought in the World War and are now homeless. Those people, commonly called "hobos", are truly hated by Shack (Borgnine), a sadistical railway conductor who swore that no hobo will ride his train for free. Well, no-one but "A" Number One (Lee Marvin), who is ready to put his life as a stake to become a local legend - as a first person who survived the trip on Shack's notorious train.

During the Great Depression, there is a community of tramps who ride the rails, and acknowledged as their "King of the Hobos" is a man known as "A No. 1." He is famous for being able to hop a ride on any train, no matter how dangerous it is get aboard or how menacing the guards. A younger tramp named Cigaret is mentored by A No. 1, and brags that someday he will take over his mantle. Neither of them has tried to board a train guarded by a sadistic railroad cop named Shack, who beats and sometimes murders men who try to ride for free. In an attempt to secure his title, A No. 1 takes on the challenge, bringing Cigaret with him, and they are not spared by the violent Shack.