The Threat plot
"The killer nobody knew. One after the other...The warning...The bullet...The corpse!"
One night, while trying to arrest gangster boss Delinko, hardened cop Steve Keenan is forced to kill Delinko in self-defense. The next day, police officer Duncan accuses Steve of having a vendetta with Delinko because he was dating his former girlfriend Laura Wallace. Steve vehemently denies this allegation, but Delinko is already the second person killed by Steve to have had an affair with Laura. Steve's brother Harry, also a police officer, assures him that everyone is happy with Delinko's death and congratulates him on another success in his police career. But then Harry warns Steve about a letter he found in Delinko's apartment.