Some of the early adventures of the lonesome cowboy. A gang operating around Nugget City is attacking stage coaches to steal gold shipments. After rescuing the driver of one of them, Lucky Luke arrives in town just in time to stop the murderous intents of a cheat. Pursuing the scoundrel after an epic bar fight, Luke finds out he's a member of the gang, and will have to arrest him and the others before riding on to new adventures on the other side of the Rio Grande.