Muggs McGinnis, champion boxer of New York City's Eastside, is scheduled to box the Westside champion. In a pool game just before the match, he pulls a fast one on Harry Wycoff, local thug, and the latter decides to have Muggs kidnapped and place a winning bet on his opponent against whoever replaces Muggs. However, Danny Lyons, runner-up in the recent Eastside tournament, takes Muggs' place and wins the match. Believing Danny is the one who had him kidnapped, Muggs tries to pick a fight with Danny, who is in love with Muggs' sister, Ivy. Danny refuses to fight in the street. Danny and Ivy win a jitterbug competition and Muggs resentment against Danny is heightened when he blames Danny for his own disqualification. Danny joins the U.S. Army but Muggs is rejected on account of his age. Muggs sets out to frame Danny on a theft charge.