This is the only episode of the series that is the sequel to another episode.
This is the second show in which a mission arises when Jim and Barney are vacationing together. The other is Death Squad (1970).
The house used here belonged to June Allyson and Dick Powell while they were married (1945-1963). This house was later used in Hart to Hart (1979).
Season six's [link=Casino (1972)], to which this is a sequel, guest starred Jack Cassidy, father of Shaun Cassidy. Ed Gilbert who plays Armsby here, would go on to play Shaun Cassidy's father in The Hardy Boys/Nancy Drew Mysteries (1977).