During the Great Depression, the US is full of people who are now homeless. These people, commonly called "hobos," are truly hated by Shack (Borgnine), a sadistic railway conductor who swore that no hobo would ride his train for free. Well, none by "A" Number One (Lee Marvin), who is ready to put his life at stake to become a local legend--as the first person to survive the trip on Shack's notorious train.