The Age of Violence (1964)

Daniel, the leader of a criminal youth gang, views new guy Victor first as a threat, then as possible addition to his gang. When Victor refuses, but sets his eyes on Daniel's Sister Nancy, Daniel orders her to get close to Victor so she can persuade him to join the gang. Daniel does not expect that instead the relationship with Victor makes Nancy longing for a life without crime. A juvenile-delinquent-crime-musical!