ickey Mouse and several other characters are on a prison chain gang, guarded by Pegleg Pete. They break rocks for a while, then Mickey breaks out a harmonica and everyone starts making music and/or dancing. Soon there's a jail-break, and Mickey's on the run, tracked by bloodhounds (including his future pet, Pluto, in his first appearance). He falls off a cliff and right into a jail cell.

Overview from themoviedb.org