Jack (Carl Brisson) is a carnival-employed boxer; patrons pay cash to take him on in the ring, and he earns the nickname “One-Round” by giving them their money’s worth with a quick knockout. His many victories have given him a big head and a bigger mouth, so when heavyweight champion Bob (Ian Hunter) shows up in town, he decides to shut Jack up by challenging him to a match. As the fight nears, Jack’s fiancée (Lilian Hall-Davis) develops eyes for Bob, giving the bout a bitter edge.
