Aunt Emma Bates (Zasu Pitts), a spinster, visits the "Big Town" to see a boxing match participated in by Mickey O'Banion (Malcolm 'Bud' McTaggart), son of Emma's old fiancé who was himself a boxing champion. At the arena Emma sits next to Terry (Roger Pryor), a reporter who is trying to track down Rex Crenshaw (Irving Mitchell), lawyer for gangster "Flower" Henderson (Tristram Coffin), who has been kidnapped by rival gang-leader Gus Hammond (Douglas Fowley), and manager of Mickey. After the fight Emma is mistaken for a notorious gun-woman named Ma Parker, and suspected by Hammond's henchmen of working in the interests of Henderson. Mickey is shot during an altercation at Henderson's nightclub and is later kidnapped from the hospital by his manager's men and taken to an East Side outlaw. Emma, in an effort to free Mickey, and with the aid of Maris (Gwen Kenyon), Terry's fiancée, decides to pose as Ma Parker.