In the middle of the night, archaeologist Charles Underwood is disturbed by a strange noise at a dig he is supervising on the Big Island. A strange masked figure appears, and tries to steal his journal. When he calls for help, including his sister Philomena (Geraldine Page), the mysterious figure vanishes.
The next day, Professor Alika Kalei (George DiCenzo) from the archaeology department of the University of Hawaii at Hilo talks to the Underwoods, suggesting that they abandon their research. He mentions threatening letters and rumours that the grave of King Hamehameha is being threatened by the excavation, and fears for their safety. Philomena tells him that they are not trying to unearth remains, and they have no interest in the grave. She says that they have spent years researching. Kalei says "We're dealing with strong feelings here."
In Honolulu, the Governor phones McGarrett to tell him that Charles Underwood is missing. McGarrett and Williams go to Hilo where McGarrett takes a copter to the excavation site, while Danno confers with the local police.
Arriving at the dig site, McGarrett tells Philomena that "the possibility of foul play cannot be ignored." He gets a radio call from Danno reporting that Charles' body has been found in a bay about a mile away. She says that she won't suspend the work, and gives McGarrett her brother's journal. After McGarrett departs, all the Hawaiians working for the Underwoods run away.
At the university, McGarrett talks to Professor Kalei, who describes the Underwoods as being as "legendary as the Leakys." Kalei is shocked that Charles' death might have been a murder. He says there is only one person alive who might know if the dig is at Kamehameha's gravesite, the descendant of one of four people who participated in the king's burial in 1819. The exact location of the king's body was a secret to keep people from taking body parts to get his powers (known as "mana"). Kalei gives McGarrett a copy of his book The Descent of the Torches, which details the ceremony where Kamehameha's body and his pallbearers supposedly descended into the ocean. Kalei's assistant George Atkins (Lou Richards) says that the grave is in lava tubes under the water, since it doesn't make sense that the torches could have burned under water. Kalei says "we are dealing with a Hawaiian legend."
At the Naniloa Surf Hotel, McGarrett asks Duke about the legends. Duke says that it's best that they are not disturbed. McGarrett pleads with Duke to "find out things none of us can," such as who is the descendant of the original burial party who might have committed murder. He wants Danno to find out who owns the land where the dig site is located. A report on Charles' body reveals that he was dead when he hit the water. There was no water in his lungs, and a severe blow to his skull.
Kalei's assistant George talks to his friend Eddie (Lee Lambert) about making "all the money in the world" by helping him to locate Kamehameha's treasures.
Danno finds out the dig site is owned by a mainland corporation, and there has never been evidence that it contains the gravesite.
In Charles' record book, McGarrett finds a description of the attacker which is "something out of Captain Cook's journal." He wants a blowup made of the descriptive artwork. A reporter for the Hilo Times, Lowry (Rex Wills, II) shows McGarrett a threatening note the paper received about the excavation site. McGarrett tells Lowry to keep this information under wraps for the time being.
George keeps up the pressure on Eddie, saying that Kalei's book tells where the grave is, but the professor doesn't know the location himself. George says that Kamehameha is buried in the lava tubes, and Charles was murdered because the excavation was getting too close to them.
When McGarrett shows Kalei the letter from the newspaper, the professor says that modern-day kahunas (Hawaiian native priests) don't believe in making threats. He says they are dignified and private religious leaders and prophets, not guardians of Kamehameha's grave. McGarrett says he wants to talk to one of them. Kalei says he can arrange an interview with one named Mahina.
McGarrett asks Philomena if her brother had any enemies. She says he had none, and no professional rivals. He suggests that she abandon the dig, but she refuses, saying she soon will be getting an extension of the grant which allows her to stay. She thinks that statistically it's unlikely that she will meet the same fate as her brother.
George and Eddie are seen scuba diving in the ocean near the lava tubes.
At the excavation site, once again all the local workers have run away. Philomena tells the crew boss to go to town and hire more.
George and Eddie try to find the land entrance to the underwater tube. Eddie says he is afraid of the "witch doctor."
Chin Ho looks for Mahina to bring him to McGarrett, but the kahuna is not available.
George and Eddie find the cave-like lava tube. Eddie falls in and twists his ankle. George goes to get help.
The sleeping Philomena is awakened from her sleep by the same chanting her brother heard. She investigates, calling out, "I'm not leaving here." She finds a small tiki statue near her cabin.
McGarrett is awakened by a knock on the door of his hotel room. When he opens it, an old woman says that "Mahina will see you now," but when he returns to leave with her, she has disappeared.
Alone in the lava tube, Eddie hears the chanting noise. He looks scared.
McGarrett drives to Mahina's house, where he is surprised in the dark by the kahuna (Nephi Hannemann).
Mahina tells McGarrett that if the islands were torn apart by a holy war, it would be over Kamehameha's body: scientists want to dig the body up, fanatics are after mana, adverturers are after artifacts and treasure, and traditionalists will shed blood to prevent anyone from touching the grave. When McGarrett shows Mahina the sketch based on Charles' journal, the kahuna says that is a ceremonial costume which he inherited from his great-great-grandfather and donated to the anthropological museum at the university about a year before.
Eddie's body is removed from the lava tube, his skull bashed in. McGarrett tells George that because he violated the kapu (or curse), now his friend is dead.
At the university, Professor Kalei tells McGarrett that George put his own interpretation on what he read in The Descent of the Torches. Mahina's costume is in the museum, the professor says that it is not under lock and key, so anyone could have taken it. McGarrett says that whoever committed the murders is the current keeper of Kamehameha's secret. Kalei says that "both deaths may have been accidental." As he leaves, McGarrett tells Kalei, "truth is always the victor."
Duke gives McGarrett four names connected with Kamehameha's burial. He doesn't want McGarrett to use these names to disclose any secrets, and McGarrett gives Duke his "solemn word" that this will be so. McGarrett analyses the long Hawaiian names and determines that Professor Kalei is the descendant who wore the costume and probably committed the murders.
Arriving at Kalei's, McGarrett finds his wife and sons mourning the professor's death, which occurred the night before. Mahina sits with the body in an outrigger which he rows away.
Meeting with Philomena one more time, McGarrett tells Danno he still doesn't know if Kalei was the murderer, but figures he was the keeper of the secret. Philomena says that she is moving on to another island. When McGarrett asks her about the tiki god which was left by her cabin, she says, "My, you are superstitious here, aren't you?" He replies, "No, just cautious."