The newspaper headline Rod is reading at the beginning refers to the prior episode "Two Birds of a Feather," and the cocaine smuggling ring Magnum helped bring down.
Peters, the Magnum look-alike, was played by Tom Lupo, who was also the stunt coordinator for a number of episodes, as well as occasionally serving as Selleck's stunt stand-in. He also did Selleck's stunts for Three Men and a Baby (1987).
The title is from the proverb: "You can't judge a book by its cover."
The music playing at the start is a direct nod to the song The End by The Doors. It is basically about parents being careless in raising children who then return come to kill them. The original is used to great effect in Apocalypse Now (1979).
Stuart Margolin ("Rod") is best known for playing Angel on The Rockford Files (1974). He also directed a number of episodes of Magnum, P.I. He is the second Rockford actor to appear in this series; another other being Noah Beery Jr..