Magnum, P.I. - Season 3 Episode 21
...By Its Cover

Rod Crysler, Thomass Navy buddy, is on parole and working as an encyclopedia salesman after serving time in California on a marijuana possession charge. The corrupt narcotics officer who arrested Rod follows him to Hawaii and threatens to send him back to prison on trumped up charges unless Rod serves a drug courier for him. Thomas offers to help his buddy out by delivering a box of encyclopedias Rod has sold, but comes in for a rude awakening when it turns out the package was filled with dope, not books, and that Rod has shortchanged one of the biggest dealers on the island. Finding it hard to believe that his friend is a dope dealer, Thomas seeks the help of Rods parole officer in locating him and setting up a sting to ensnare the corrupt cop and the drug dealer, thereby clearing Rods name.