Anyway, Freebairn-Smith and the show parted ways, and probably not amicably, since in a later episode, creator Donald Bellisario made a rather gruesome reference to his name:
HIGGINS: Agatha, did I ever tell you the story about Lieutenant Smythe?
AGATHA: Wasn't he the one who was eaten by a tiger?
HIGGINS: No, that was Lieutenant Freebairn-Smith.
And midway through the first season, we start to hear the new theme, by Mike Post and Pete Carpenter, over the closing credits; and by episode twelve or so, it's established as the sole theme song. And once that song is played over the opening credits, suddenly the whole show seems to work better, because the theme puts us in the right frame of mind to see a Magnum story: instead of telling us that this is some cheesy private-eye show that happens to take place in Hawaii, it tells us that this is a show about a really cool and fun character.
One reason why Mike Post was such a good writer of TV theme songs in the '70s and '80s (his work in the last ten years or so hasn't been as good) is that he understood that successful TV shows are about characters, not situations, and that therefore a good theme song should introduce you to the characters. He once explained that his theme song for The A-Team was based on what he knew about the characters: they were fun-loving action heroes with a military style, so he created a jaunty military theme for the main melody; and they were Vietnam veterans, so he wrote an electric guitar solo, which is TV-music shorthand for "Vietnam flashback." One might argue that any show that includes Mr. T does not deserve to have even that much thought going into the creation of the theme song, but you have to admit, it works. Post and Carpenter's theme for a better Steve Cannell show, The Rockford Files, is basically a character portrait: the quirky melodies and orchestration signal that this is a show about a different, less conventionally heroic kind of hero.
And Magnum is the same way. The pulsating opening theme, the string tune that follows it, the electric guitar solo, all tell us to expect something from the main character (he's adventurous, he's romantic, he's a Vietnam vet) and from the show itself (a mixture of several different styles). Using pop tunes for the opening, as some shows do nowadays, or using some generic-sounding atmosphere-setting theme, just doesn't work as well as a theme that conveys what the show is about and who this show is about. Of course it helps that shows had fewer commercials in the '80s, which meant that they could and did devote a full minute or more to the main title, whereas today's shows, with their shorter running times, need shorter credits and shorter theme songs.
One other thing about re-watching Magnum is that it reminds me again that I have a soft spot for the work of Don Bellisario (creator of Magnum, Quantum Leap, Airwolf, JAG and many more). Not only is he one of the last producers of this kind of old-fashioned adventure-drama show, but he doesn't condescend to the format, and is frequently willing to surprise his audience by playing tricks with the formulas that the audience has been conditioned to expect. The ending of his Magnum episode "Echoes of the Mind" (included on the first DVD set as a bonus, though it's actually from the fifth season) is still one of the most surprising things I've seen on this kind of TV series, but it wouldn't be particularly surprising in an HBO show, let alone a novel. It's a surprise because we, the viewers, have come to expect a network TV action-adventure show episode to end a certain way, and the writer, Bellisario, takes advantage of that by going against our expectations. The events of this episode also carry over into the next week's episode ("Mac's Back"), which unfortunately isn't on DVD yet, but that's another little reversal of our expecations, since at the time that episode aired, shows like this never had any carryover from one episode to another.