A diver swims among Hawaii's marine life searching for something. Presumably finding it, he heads to the surface.
Through the saltwater aquarium a large group of friends sing "Happy Birthday" to Mingo (Jay Robinson). They gather in a yard with a large table with a pile of gifts on it. Mingo is kind of an ass telling people not to crowd him. He opens his first gift: a kukui nut lei from Tommy. He opens the second gift and reads the attached card, "Happy Birthday Pilau Kane, Mingo. It is your last". There isn't a signature to the note and Mingo is clearly perplexed asking his associate Akamai (Ray Danton) what the Hawaiian words mean. Akamai tells him to move on and not to worry about it. Akamai finally translates the message as "filthy scum" gathering gasps from several attendees. Mingo opens the box and handles the tissue paper inside. Afterward, Mingo collapses, choking, and dies.
Ambulance attendants load Mingo's body into an ambulance as Doc (Al Eben) stands by. McGarrett and Five-O arrive on the scene as the team start inside. McGarrett speaks to Doc who tells McGarrett something hit Mingo's central nervous system. Doc says the autopsy will be interesting. McGarrett walks inside.
Danno briefs McGarrett in the yard showing him the note Mingo was reading when he collapsed. McGarrett and Danno survey the crowd, the bottom feeders of the world. Danno goes in search of the typewriter used to write the note. McGarrett talks to Mingo's partners: Akamai and another man (Jason Evers) who tells McGarrett one minute things are going well and the next, Mingo is dead. McGarrett wonders who stands to profit from Mingo's death, suspecting Mingo's two partners asking them outright who gets his piece of the "real estate shill game". Akamai doesn't help their case by saying they will now split things two ways and not three. McGarrett isn't impressed asking the assembled partygoers to recreate the scene just before Mingo collapsed. As the crowd follows McGarrett's directions, Danno walks out after finding the typewriter used in the den. The paper is normal stock and Che Fong (Harry Endo) is already dusting for prints. The crowd gathers as before and as McGarrett walks them through what happened next, they realize the box Mingo was opening has disappeared! Worse yet, no one saw what was in the box and no one knows what happened to it. McGarrett become less impressed at every passing moment. The other partner recreates the noises Mingo made prior to dying and McGarrett asks again if anyone touched him. Turns out, Mingo had a thing about people touching him. McGarrett tells everyone to sit down. He then changes tactics: how many people have the trio swindled over the years? McGarrett is looking for motive and has 4000 people right off the bat in the customers sold bad real estate. Mingo wasnÕt a nice man but people came to the parties because he asked them to. McGarrett wants things wrapped up telling everyone to go home. "The party's over".
Doc is nearly giddy because Mingo's case it quite unique but Danno and Kono, not so much. After Doc performs an autopsy, he doesn't know what caused his death but he has been able to eliminate natural causes, a disease of the nervous system and "cerebrovascular accident". Doc says he suffocated and found unusual hexagonal alkaloid particles present in Mingo's blood: an ammonium derivative. Doc suggests that Mingo was poisoned causing "paralysis and suffocation," but there are no obvious signs as to how this was done because he didn't ingest it and it was found only in the blood. Danno is confused because how did it get into his blood. Doc says there were no marks, abrasions, or any noticeable means of entry. Danno has had enough because they need to know what the poison was, how it got into Mingo and they need to know right away! At least they know it was intentional.
Later, Akamai shows his partner a threatening typed message that he received. Akamai isn't concerned as he frolics on the beach with a couple of bimbos. His partner yells after him about being crazy as Akamai swims in the tide pool. The partner isn't messing around, he calls Five-O.
Danno and Kono show up at the house with Akamai not believing his partner called Five-O. Akamai is still not concerned about the threat on his life but his partner is edgy. Danno has no patience left demanding the note with Akamai tossing it to him. The partner gets in Danno's face because the death date in the note is for tomorrow! Akamai tells Danno he received it under his bedroom door and found it "when we got up". Kono wonders who put it under the door asking Akamai if he has any ideas but no luck there. Danno turns to the other partner, Wallis, who claims he was asleep but the partners turn on each other accusing each other of trying to out smart the police. As Wallis freaks out on Danno, Akamai calls out to Manoa (William Valentine), their butler suggesting they go fishing on the reef. Akamai is straight with Danno: he isn't worried about the threat and if Danno wants to watch him, he has to go out into the water. Danno turns him down and Akamai walks away with the girls. Danno and Kono follow Wallis inside the house with Kono stopping at the aquarium. A dead fish, a yellow Tang, floats in a tank fascinating Kono on the same day Mingo was killed. Danno blows off "the deep Hawaiian symbolism" telling him to check out Akamai's room while he looks into Mingo's.
Wallis leads the way showing Danno a videotape machine in a bedroom, which he says is "a sales tool". Wallis plays the tape with lots of beautiful scenery but it is nowhere near the property the trio owns. Danno warns Wallis it's only a matter of time before the trio, now pair, will slip off the "tightrope" they've been walking. Danno asks why the camera is in the bedroom and Wallis answers innocently it has to be somewhere. He goes on to explain Mingo liked to watch rather than participate. Danno is grossed out ready to nail Wallis, even if it is for pornography.
Danno walks out of the house with Kono, leaving an HPD officer named Paul (Arte McCollough) to keep watch. He orders around the clock presence and promises to send relief later. Danno radios into McGarrett briefing the latest.
Akamai and Manoa sail out to go skin diving with spears in order to fish. Just after spearing a fish, Akamai almost drowns trying to pull out the spear from under a rock, but Manoa sees what's happening and saves him. Manoa is able to drag him back to the surface and the sailboat. Back on shore, Wallis and the girls meet Akamai and Manoa. Akamai is extremely grateful and as a sign of gratitude, he gives Manoa his expensive watch. Meanwhile, the sparring between Wallis and Akamai continues.
In McGarrett's office that night, McGarrett is perplexed by the case, even when Danno and Kono say there's resentment but no motive for murder. Chin runs down the staff. The cook is Chang Lu (Yankee Chang), age 52, bachelor and worked several jobs at "some of the best hotels" but changes them a lot. The houseboy is Jack Manoa, local, 43, married with one child who is deceased and has worked as a fishing guide. The maid is Kyo Sasaki, married with two children and her husband is a successful fisherman with a fleet of five boats. She works off and on "as a domestic". Chin says all three are clean but McGarrett wants more: such as why the job changes, what happened to the daughter and why does the maid have to work as a maid? Danno reminds McGarrett if they have to look through the customer list for a motive, it's going to be rough. McGarrett knows this and tells them about a meeting with the Attorney General who is aware of many lawsuits and complaints but no threatening letters regarding the trio's real estate activities: "one royal swindle".
The next morning, a second fish, a Potter's Angelfish, floats in the aquarium next to the yellow Tang. Wallis stands on the balcony drinking as the maid has a tray ready to serve Akamai. As she enters his room, she screams, discovering him dead! The two HPD officers run from downstairs and Wallis freaks, yelling to call Five-O.
Danno arrives to take charge of the ongoing investigation. Wallis is "scared out of his gourd" jumping into Paul's HPD car. Danno gives him a choice: walk or be carried. Danno and Paul walk him back inside where Che is already at work collecting evidence in Akamai's room. Kono notices something weird with the pillows while Danno goes over the logbook of the comings and goings from the night prior. The girls slink around the corner as Danno speaks to the staff when the maid quits right then and there. Danno tells her to keep herself available and she has no intention of going anywhere but she's out of the house. Wallis picks up on the maid's actions wanting to leave the islands, becoming more and more paranoid, but Danno says Wallis is not going anywhere since he is "suspect number one" and "target number one." Danno isn't messing around yelling at Wallis he had both opportunity and motive! Danno isn't impressed with Wallis one bit offering him a cell downtown with "steel bars". Wallis bristles at the thought of walking voluntarily into jail but he's quickly running out of options. He decides to stay at the house taking each girl, Eadie (Shannan Kincaid) and Donna (Cathy Musket), on the arm. Danno watches them walk away but asks quickly where the girls were when Akamai was killed. This launches Wallis higher into orbit with his paranoia!
Danno walks into Akamai's room where Kono figures out what's going on with the pillow: it's wet with seawater. Che takes it along with everything else to the lab. They walk out where Danno verbally jabs Wallis one last time, "hope I didn't spoil your fun and games". Danno orders the manpower doubled, two men inside and two men outside to seal the house off. Kono stands by the aquarium again seeing two dead fish, maybe soon three. Wallis walks away in disgust wondering if Kono is a cop or fortuneteller.
In the lab, Doc joins Che ready to brief about "some goodies". Doc ran several more tests to determine that a deadly poison like curare, which paralyzes the nervous system, was used to kill Mingo and Akamai. Che then confirms Akamai's pillowcase did have seawater on it as well as the note Mingo received when he was opening his presents. Kono verbalizes his hunch there was a connection between the dead fish and the dead men. Danno isnÕt ready to embrace it completely thinking it's all superstition. However, McGarrett follows the train of thought and orders Danno to find what kills people and fish living in the sea.
Danno and Kono visit Sea Life Park, where Dr. Pell (John Hunt) explains a shellfish called Cloth of Gold can paralyze a grown man in less than 60 seconds. It's shy by nature but will turn "vicious killer" if surprised poisoning fish, other gastropods and even each other! The doctor explains the aperture: minute needles leaving no marks but remains in the tissue. The victim may feel a slight sting, maybe nothing. Danno asks about the poison being an ammonia derivative and when Dr. Pell confirms this, they have their answer about what's been happening "learning the hard way". Danno tells Kono to get with Doc to look on Mingo's hand and Akamai's face, scalp and neck. He then borrows the phone to call Paul to check on Wallis.
Paul talks to Danno as the second HPD officer (Roland Naauao) stands by. Wallis has locked himself in his room! Paul yells up to him to double-check he's okay. Wallis gruffly answers back being half-drunk. Danno overhears some of it and when Paul comes back Danno tells him no one goes near the aquarium because they're on the way. Paul laments about being on the force five years and he has to "guard a fishbowl" with his partner pointing out the two dead fish.
Danno and Kono rush to the house. Meanwhile, Manoa brings Wallis his dinner passing HPD inspection prior to entry. He hands Wallis a Cloth of Gold shell as a gift. As Wallis starts to feel the effects of the poison, Manoa tells Wallis about a young girl named Tia, "as pure as a plumeria flower".
At Five-O, Chin runs in looking for McGarrett who is in a budget meeting according to Jenny (Peggy Ryan). He asks where Danno is and she tells him he and Kono were on the way to Sea Life Park. Chin gets on the phone for a patch. While this happens, Manoa keeps reminding Wallis about Tia, his daughter. The trio drugged her, filmed her participating in pornographic activities, and turned her into a hooker. Chin was able to dig up she died of infectious hepatitis only five months before due to a dirty needle. She was only 16! Chin says it happened at a party, Danno can imagine where it was held and he's pretty ticked about it.
Manoa picks up the Cloth of Gold after Wallis dies walking out of the bedroom. Danno and Kono then arrive at the developers' house, noticing that the Cloth of Gold shell is gone from the three aquariums. They run to the room where Wallis locked himself into where Kono breaks in the door but they're too late.
Manoa attempts to flee to the Big Island on a yacht, but Danno trails him in a helicopter and McGarrett and Kono on a police boat. Danno spots him, directing the HPD Harbor Police boat to him. McGarrett and Kono eventually catch up to Manoa with McGarrett boarding the yacht. But Manoa has the Cloth of Gold shell, which he touches to his throat, committing suicide. Manoa falls off the yacht into the water.
This plot summary Copyright Bobbi Baker & Mike Quigley ©2019. No reproduction of any kind without permission.