The Alfred Hitchcock Hour - Season 3 Episode 10 Memo from Purgatory

Jay Shaw is a young writer interested in writing a book on juvenile delinquency. He changes his identity and infiltrates a particularly violent gang named "The Barons". He manages to get the trust of Tiger the leader of the gang but trouble arises, when Filene, Tiger's girl friend, falls in love with him. Filene's love, however, is not the only source of tension. Other gang members grow jealous of Jay's growing power within the gang. When gang members break into his room and find his notes, they tell Tiger that Jay's an undercover cop. Jay is sentenced to death by Tiger and the gang. He manages to get away, but in the process Filene is killed. The murder is witnessed and Tiger and the rest of the gang are hauled off to jail.