Danny Di Pace, Arthur Reardon and Anthony "Batman" Aposto are members of a street gang named the Thunderbirds in New York City in Spanish Harlem. They have a ongoing turf war with a Puerto Rican gang call the Horseman. The three Thunderbirds unleash a knife attack on Roberto Escalante, a blind member of the Horseman and stab him to death. They are caught and arrested, and during questioning by the police and an assistant district attorney, Hank Bell (Lancaster), Bell discovers one of the boys is the son of an ex-girlfriend (Shelly Winters).
Back at the office of the district attorney Dan Cole (Edward Andrews), Bell admits he knows the mother of one of the suspects in the killing but despite objections, he is not taken off the case and admits that he in fact grew up in the same neighborhood. At the funeral for Roberto Escalante, he is confronted by his ex-lover and she tells him her son promised he would never join a gang. Bell then sets out to find out the true facts about the killing and admits that he changed his name from Bellini to Bell because he was ashamed of his background and where he grew up.