Watch Fmovies. During a rebellion of prisoners at the San Quentin State Prison, Boston Blackie makes a lightning escape aided by Mary McGinn while chased prison guards. Mary is a school girl, unaware that her brothers are crooks. She is expelled from school. Blackie rejoins his gang and takes refuge in Mother McGinn's house, where he again meets Mary. She devotes herself to making Blackie go straight and wins her point.