Margie Regan makes her first appearance in the recurring role of Claire Townsend, the girlfriend of Detective Bert Kling. In the novels on which the TV series is based, Claire was killed off. Author Ed McBain would later say that he received his highest number of letters in protest ever because of that plotline.
The character of informant Danny Gimp frequently appeared in the novels although this episode marks his only appearance of the TV series.
Claire: Bert, the car's the other way.
Carella: (to Kling) He shot first. You just remember that.
Meyer: (about the shooting) You don't get over it. You adjust to it.
Meyer: I've always said--where would we be without you lab guys.
Claire: (to Kling) Bobby Matfield didn't have to kill you. You're doing that yourself.