Ignoring Inspector Farraday's friendly advice to stop helping women, Boston Blackie goes to the rescue of a female being attacked by two men. She is Geraldine "Gerry" Peyton, an old flame of his. She begs him to help protect her baby from her husband John, who has just been paroled.
When John finds them together, he assumes that the child is Blackie's and draws a gun. A fight ensues during which an unseen third party shoots John. Acting on an anonymous tip, Farraday arrives soon after and assumes that Blackie is responsible for the dead body. Blackie has his sidekick, the "Runt", hide the baby at the apartment of the Runt's girlfriend, Mamie Carleton.
Blackie escapes from dimwitted Sergeant Matthews. An investigation soon arouses his suspicions. Gerry and Smiley Slade are trying to swindle her wealthy father-in-law Cyrus Peyton. The child is actually her brother Hack Hagen's. They framed Blackie in order to make John disappear. When Hagen tries to renege, worried that he will not be given his son, Smiley shoots him.
Disguised as Cyrus, Blackie goes to see the pair. He manages to overcome Smiley only to have Farraday break in, arrest him and let Gerry and Smiley go free. However, it is all a joke on Blackie. For once, Farraday has determined the identity of the real crooks. When Blackie goes downstairs, he sees the pair in handcuffs.
