Baby-Face Mouse, disobeying his mother, goes into the territory of Rat Enemy No.1. The gangster is working on turning the young mouse into a member of his gang, but Baby-Face gets so tough he knocks out Rat Enemy No. 1 and turns him over to the police and gets a reward. Back home though, he gets spanked for crossing the railroad tracks into bad territory.
Mother Mouse warns her son Baby Face to stay in the yard... so the first thing that he does when Mom's eye strays is wander across the railroad tracks. In no time, he encounters Rat Face the wharf rat, who runs a school for crime in which the subtle art of picking pockets is matriculated. Baby Face is a very apt pupil, but he displays a disturbing sadistic inclination, which he directs at the hapless Professor Rat. After several minutes of mayhem, Rat Face winds up in the hoosegow, and Baby Face receives a much-deserved commendation for his capture.