After Mickey gets over the prison wall, he tries to run away, but is pulled back by the weight of the ball and the chain breaks, yet Mickey still carries the ball when he could just run away and leave the ball.
Obviously, our celebrity mouse has committed some atrocity to be put in prison and forced to break rocks on a chain gang. He never claims his innocence.
Because of the boredom of his guard, Mickey is able to start playing his harmonica and getting all the other prisoners involved. Soon there is a jailbreak and he is caught in the middle. Good Mickey Mouse episode.