Although Colleen Moore made this drama before Flaming Youth, it came out later, which wound up being a big help at the box office because it was able to bank on Moore's newfound stardom. She's billed at the top of the credits, but it's really Forrest Stanley who, as Boston Blackie, has the lead. The scenario was based on Jack Boyle's tale, The Daughter of Mother McGinn, part of his series of Boston Blackie stories. Boston Blackie has escaped from San Quentin and when he saves Mary McGinn (Moore) from a runaway horse, she decides to help him out. She finds out through Blackie that her father, now dead, and her brothers are all crooks, something that has been hidden from her by her mother (Margaret Seddon). Mother McGinn has been running a boarding house to pay for Mary's expensive schooling, but when the institution finds out about her background, and that she helped an escaped con, Mary is expelled. Mary has fallen in love with Blackie and will do anything to make him go straight -- even join his gang. Her action wakes him up to his wrongdoing, and Mary convinces him to complete his prison sentence so that there will be nothing standing in the way of their future.