Cosmo Jones, Crime Smasher (1943)

Cosmo Jones, a detective from a small town who learned his trade through correspondence courses, arrives in the city hoping to work with the police. He witnesses a murder committed by a rival gang. Meanwhile, socialite Phyllis Blake is involved with a gangster named Tom, and the opposing gang plans to kidnap her. Cosmo is with Sergeant Flanagan when the kidnapping attempt occurs outside a nightclub, resulting in a bystander being seriously injured during the ensuing gunfight. Police Chief Murphy blames Flanagan for the incident and demotes him. Cosmo, with help from a porter named Eustace and Flanagan's fiancée Susan, investigates the murder. Phyllis is eventually kidnapped, and Cosmo concludes that one of the two gangs is responsible. He has her father place a newspaper ad stating that contact has been made with the kidnappers. Both gangs believe the other is betraying them, leading to a complete elimination of one gang by the other.