Someone is trying to murder Elmo Ziller, Higgins' illegitimate half-brother from Texas. Elmo has brought his rodeo to Hawaii and Magnum is asked to protect him.
Higgins swears that he has a half-brother who is an eccentric guitar-playing rodeo owner, but Magnum believes himself to be the target of a prank and is not sure how to react when he is asked to protect the man.
- Tom Selleck as Thomas Sullivan Magnum IV
- John Hillerman as Jonathan Quayle Higgins III
- Roger E. Mosley as Theodore "T.C." Calvin
- Larry Manetti as Rick Wright
- Robin Dearden as Lexi Ziller
- John Dennis as Gunman
- Med Flory as Gunman
- Barbara Rhoades as Marcella Ziller
- Glenn Cannon as Dr. Ibold
- Gillian Dobb as Sylvia, the Desk Clerk at the Belvedere Club
- Benjamin C. Jaus as Police Officer, serving subpoena (credited as Ben Jaus)
- Henry Kapono Ka'aihue as Dan (credited as Henry Kapono)
- Carolyn Shofner as Cowgirl
- John Hillerman portrays his usual role as Higgins as well as that of his half-brother, Elmo Ziller, who hails from Hondo, Texas. That Elmo Ziller is a Texas is no doubt an in-joke on behalf of Magmun's producers, because although the character of Higgins is well established as being British, Hillerman himself was born and raised in Texas.
- Magnum: Howdy part...(laughs)... No, I can do it! I can do it! ... Here goes. Howdy partner, (laughs) you just ride into town? See, I'm headin' up to the ranch house to see Higgins. So you just be still and say right there... (chuckles)
- (Magnum is determined to find out if Elmo is really Higgins or not)
- "Elmo Ziller": What the hell are you trying to pull?
- Magnum: I wanna pull your mustache!
- "Elmo Ziller": You wanna what?!
- Magnum: Higgins ... Higgins, listen to me. How ever you're doing this, why ever you're playing this game with me, stop it right now. Don't ride this [Bronco]. Look I know your pride, but you can quit right now.
- "Elmo Ziller": Let her rip! (rides Bronco)
- (to Magnum)
- "Elmo Ziller": You must bring me the head of Marcela Ziller.
- (to Magnum)
- Higgins: You have more "dumb luck" than anyone I know.