It's 1851. Just Baggot (Wallace Beery) is a horse thief and general criminal. The San Antonio-San Diego Mail Line is called the Jackass Mail. It is one of the earliest stagecoach mail service. When Baggot encounters the Jackass Mail, he tries to rob it, but another gets to it first. He ends up shooting the robber who killed the driver. He joins owner Clementine 'Tiny' Tucker (Marjorie Main) as the new driver. He befriends young Tommy Gargan, son of Red Gargan who turns out to be the robber.

I expected Beery to do a road movie with the boy. The boy was always going to find out the secret sooner or later. This has a lot more with Tiny. She and Beery have a lot of ups and downs. Marjorie Main has good comedic touch. I'm just not that into the romantic pairing. This is fine.