The title of this episode and the name of the [fake] Hawaiian island featured in it, “Kapu”, roughly translates to ‘taboo’ in English. But I think a more descriptive title would be “Magnum goes (even more) Hawaiian”, as this is probably the most Hawaiian of all the Magnum, P.I. episodes.
The episode starts with a bunch of Hawaiians arriving in a canoe at Honolulu harbor to unload some cargo. They have a young girl (woman?) with them who goes off to the Aloha Tower and on the way passes Magnum talking on the phone.

From there, things escalate quickly. A guy that Magnum is supposed to pass on some documents to, runs away after seeing him, and then gets shot by someone else who was waiting to assassinate him. The Hawaiian girl witnesses the murder, and Magnum grabs her and they run off in order to evade the assassin. They jump into the water in the harbor, but the bad guy shoots into the water and we see blood.
The next thing we see is Magnum waking up in an unfamiliar place. The mystery becomes trying to figure out where he is and why he’s there. And after meeting the Hawaiian woman who’s taking care of him, it becomes clear that the Hawaiian villagers are not about to let him leave. So why are they keeping him? And how will he ever escape?
. . .
There’s a lot going on in this episode. For one, because Magnum has the reputation of being unreliable, none of Magnum’s friends are worried about him being missing until several days later.
Rick’s cousin Rita is in town, and Rick thinks that Magnum has gone into hiding in order to avoid having to meet her. Higgins meanwhile thinks that Magnum is just shirking his responsibility of being his assistant at the museum.

Back in the village, there’s lots of scenes with Magnum waxing poetic about darkness, and waves crashing, and growing terror. And lots and lots of scenes of the girl creeping at him through the window to his room.

Since everyone is being mysterious and won’t even admit that this girl exists, Magnum is desperate to get away and tries to escape in a canoe, but they end up chasing him down and bringing him back to the village. At this point, he gives up and turns his pants into cutoffs.

One of the most WTF lines delivered in the episode comes after Magnum once again asks “Why won’t you let me see the girl?”, at which point he’s told:
If you’re feeling so frisky, why don’t you do something to help?
So we are then regaled with a montage of Magnum digging holes, casting fishing nets, and creeping on a group of young women bathing in the ocean.

Meanwhile in Honolulu, Rick gets in a car to talk to Icepick about Magnum. We see the car being driven forward, Icepick tells Rick about the assassination and a Hawaiian girl being a possible witness, and when Rick gets out of the car we find that it’s still in the same spot. (Wait what?!)
So that’s followed by a montage of Rick looking for Magnum, interspersed with the bad guy trying to find out where the girl might be based on some shells from a necklace she had dropped at the time of the assassination.
Eventually Rick figures out Magnum must be on the Hawaiian island of Kapu [which doesn’t actually exist]… probably because Rick and Magnum have a telepathic connection.
Soon after, Magnum actually catches the girl sneaking out of his room, and learns that her guardians have been putting stuff in his food to keep his mind clouded so that he wouldn’t remember her.
Since Magnum now knows the girl exist, he is invited to the luau where he watches her dance the hula and they give each other the lovey eye.

After the girl finishes dancing, they go off towards the beach, at which point the bad guy has arrived in a motor boat with a gun. After a bit of a scuffle, Magnum saves the day, with the help of Rick, TC and Higgins arriving in the helicopter.
The episode ends with Magnum saying goodbye before taking a canoe back to Oahu with the girl’s uncle, probably because doing this is more manly than taking the helicopter back with Rick & co.
