In Hawaii Volcanoes National Park, a guy (Richard George Carter) sets charges at certain points as another man (James Olson) supervising the goings on. There are actually two guys, one being Kalani (Liwai Napuelua Jr.) and the first guy, setting charges and wiring them into a timer that is remotely started. The supervisor sets the timer after sending the pair back to the truck to clean up the mess. He places the timers in a ditch so they're not obvious from the road and he covers them with foliage. The pair is nearly done when the supervisor shoots them causing them to collapse into the truck bed. The supervisor covers them and drives them to dump them into a volcano vent!
When the supervisor drives home, he notices a dark Mustang in the driveway and stops momentarily but proceeds anyway. He walks into the house calling for Doris (Sheree North) who sits on the lanai with another man (Felice Orlandi) who he immediately recognizes as Bonner. Bonner is in Hilo to make sure Sam Kaina gets his money back. Doris wants to know about what money and Bernie tells her it's "chicken feed," which Bonner wants now "if it's just a little loose change". Bonner doesn't want to stick around Hilo until Thursday when Bernie will have the money. Bernie leads Bonner away trying to figure out why he stopped by the house with Bonner explaining he's been told to stick to Bernie until his $25,000 loan is paid back with $47,500 in interest! Bonner tells him they'll back off once the entire $72,500 is paid back. Once Bernie walks back inside, Doris confronts him about Bonner being "a collector from a loan shark". Doris wants to know how much they owe "this time" with Bernie telling her. Doris flips out yelling at him that he didn't learn his lesson when they left L.A. but Bernie is confident he'll have it and more by Thursday.
Jenny (Peggy Ryan) calls into McGarrett with the governor on Line Four. He's in Kona wanting McGarrett over on the Big Island as soon as possible because he's received a threat from "some damn fool" who's threatening to trigger a volcanic eruption wiping out half of the island! That is unless the fool receives $500,000 from the state. McGarrett can't believe it but says he's on the way.
Doris keeps going off on Bernie not believing anything he says because she sees their lives as hopeless, still under the thumbs of loan sharks. She wants to live a normal life and doesn't see that happening. She slams the door in his face yelling at him to leave her alone but he's determined to see it through.
A Hawaiian Airlines jet lands at Hilo with McGarrett going to meet with the governor and sending the team to Park Headquarters. The helicopter pilot (William Gordon Lacy Jr.) takes McGarrett to Kona landing in the Kona Surf entrance.
McGarrett reads the note the governor received wondering if it's possible and they know only one place has the answers: the Volcano Observatory. McGarrett and the governor fly out to the observatory meeting up with Dr. Rogers (Seth Sakai) who briefs them the guy knows his business. "The northeast rift lies directly upslope from Hilo" and a large lava flow could reach the city. When the governor asks what's the worst case, Dr. Rogers shows film from prior Kilauea eruptions doing some serious damage with hot, fluid rock flowing everywhere including exploding into the sea. The flows have been clocked as fast as 35 miles per hour! Dr. Rogers warns a massive flow could destroy Hilo in less than a day. McGarrett wants the park closed immediately to prevent an accidental triggering. He also wants an Air Force reconnaissance flight with infrared to see if there are in fact explosives are planted along the rift. The governor will call Hickam Field right away and he plans to notify Civil Defense. Dr. Rogers offers his help with McGarrett wanting to know what type of explosives would be needed, where they would have to be placed and in what quantities. While Dr. Rogers doesn't have anyone on his staff with that expertise because they know the geology not the explosives side but he mentions Consul Oil Company has brought a man out about a year before to study the possibility of using geothermal energy: it's Bernie!
Bernie surveys the area with McGarrett telling him it would take quite a bit of dynamite to break open the rift due to "the lava's quite far down". Bernie tells McGarrett about 30 to 40,000 pounds of dynamite would be needed and a whole team would be required to set it up: no way an amateur did this. Bernie estimates it would cost about $250,000 to put the plan together with eight to ten men. McGarrett doesn't buy what Bernie is dishing out because if it cost $250,000 why only ask for $500,000? McGarrett figures it's a hoax or someone has found "some bargain basement explosives" as the reconnaissance aircraft flies overhead.
McGarrett and the team set up shop at Park Headquarters trying to figure out what's going on. Danno reports all government agencies and private companies handling high explosives have accounted for all their materials. Chin reports the same for the military. As the team kicks around ideas, Bernie listens in standing next to the window. McGarrett figures it must be a small operation and the explosives attained cheaply. Ben wonders what with Danno saying the operation can start with raw materials due to some fertilizers contain the right mix to "form a base". Danno mentions thanatine nitrate and all it would need is diesel fuel: both are plentiful on Hawaii. Danno says the mix is 80 percent as powerful as nitroglycerine. McGarrett confers with Bernie who says it may be far-fetched but it would work. McGarrett sets Chin onto the fertilizer wholesalers and distributors to uncover any bulk buys especially "non-commercial" sales. Then he puts Ben on tracking the diesel fuel suppliers, calling the Honolulu refineries if necessary. Bernie excuses himself with McGarrett asking him to "stay on tap" in case they need him again and he's all too happy to oblige.
Bonner returns to Bernie and Doris' house offering to fix her a drink but she doesn't drink. However, Bonner makes a move on her and she doesn't necessarily resist. Meanwhile, Bernie puts the evidence of the fertilizer bags into his truck as Chin and Ben check out the distributors for the explosive ingredients!
McGarrett and Danno walk the rift with Danno saying if they knew where the detonator was, he might be able to diffuse it. When Danno trips, he sends a rock crashing down onto a landmine but it's not the trigger and it tells McGarrett this isn't a hoax. They back off, for now.
At Park Headquarters, the aerial photos are in as McGarrett briefs the governor: there are about 36 charges set about surrounded by 25 landmines! Their problem is the detonator: where and what is it? The governor wonders if an Army demolition team could help with McGarrett saying one on standby wouldn't hurt. The governor will contact the Army for that and he wants McGarrett's helicopter to pick him up in Kona to go to Hilo.
Ben reports back that the diesel distributors didn't sell any large amounts of fuel to non-commercial users. Ben checked Hilo and Kona, waiting on a call from one in Kona. Chin walks in with a possible break with Krider Chemical Company: they sold enough thanatine nitrate "to blow the whole island". The phone rings for Ben who takes it in another office. McGarrett notices two names: David Kalani and Peter Herberts, a pair of laborers. Chin says between the two they bought 40,000 pounds of the fertilizer at 1000 pounds at a time from January until a couple of weeks ago. Chin explains they tracked them down but couldn't question them because they're missing. Ben walks back in to report five non-commercial users and one bought enough fuel "to run an aircraft carrier for a week": one "Mr. Bernard Brown".
Bernie returns home walking in stripping off his clothes finding Doris asleep on the couch. Meantime, Danno and Chin check on Bernie at his place of work with the man (Roger S. Ritchie) telling them Bernie "is a genius when it comes to geothermal dynamics" but has martial issues because of money: he lives "about ten paces further" above his means even though he's paid $40,000 a year. He tells them about the scrap in L.A. when the company bailed him out and transferred him to Hilo. Looking through his file, Danno points it out to Chin: he served in the Korean War with the Air Force specializing in "demolitions".
Bernie continues to clean up dumping his clothes in the hamper and taking it out to the garage. He doesn't do it completely quietly, waking Doris. As he dresses they argue again about the $72,500 with her hoping Bonner breaks every bone in Bernie's body. When she says she's through with all of it, he pulls out a copy of the letter for the further instructions. He lays out his plan to her: they'll take a flight to Honolulu to connect to a flight to Hong Kong and five minutes before they leave, he'll tell the governor how to diffuse the detonator. She is shocked and as Bernie leaves, she calls Bonner.
McGarrett meets with the governor who has received the further instructions. He tells McGarrett Hilo National Bank is prepping it as they speak. The governor wonders why they need to pay the money if they're sure Bernie is the guy responsible. McGarrett explains they don't have a lot of choice because even if they pull Bernie in, he could clam up and not tell them how the explosives are triggered. McGarrett also believes Bernie is over the top desperate for the money and they have to be ready to pay off. McGarrett plans to speak to Bernie again to gain a feel for whether he can be trusted or not. The governor wants McGarrett to handle the payoff personally with the money to be sent to Park Headquarters. Danno radios they're about ready to take off: the plan is to stake out the northeast rift from the air. McGarrett tells Danno if he spots Bernie to stay far enough away to prevent scaring him off as the helicopter launches. He then tells Chin to "bring the car around". The governor wishes McGarrett luck.
Doris anxiously waits at the house as Bonner pulls up. She throws her suitcase into the back seat explaining as they drive off what's going on. At the same time, Danno keeps his eyes open for Bernie at the northeast rift as McGarrett and Chin arrive at Bernie's house. They knock on the door with no answer and it's locked, which is the same for the garage. McGarrett finds the remote for the garage successfully opening the door. Inside, McGarrett finds the dirty clothes with the fertilizer all over them and takes them for evidence. He pushes the remote to close the garage and tosses it back into the convertible parked there.
Danno spots Bernie on an access road and radios McGarrett about the progress. Danno keeps him in sight as Bernie stops, gets close enough to activate the detonator via remote and leaves. Danno reports Bernie is leaving the rift area and heading for the coast at the same time Ben runs out with the money. McGarrett takes off and Bernie waits at the sugar mill for the drop. McGarrett arrives with money leaving the briefcase in a second story hallway. At the pre-determined time, Bernie goes in as Danno watches everything from the helicopter, reporting to McGarrett.
Inside, Bernie makes a grab for the money only to be interrupted by Bonner and Doris! Bonner tells him they're going to split the money and leave Bernie behind. Doris told him she was through and she meant it! When Bernie refuses to turn over the money, Bonner shoots him twice and grabs the briefcase running out of the mill. Doris follows Bonner out leaving Bernie for dead. At his back up point, McGarrett wants a report from Danno: he sees nothing until he spots Bonner and Doris with the briefcase heading for Bernie's truck. McGarrett tells Danno to stop the pair as he heads back to the mill. As Bonner makes a run for the truck, they knock him over with the helicopter! McGarrett arrives back at the mill finally finding Bernie trying to crawl/drag himself out of the mill. McGarrett asks him how to stop the explosion but Bernie dies before he can tell him anything.
Bernie's body is taken away as McGarrett talks to Doris but she's no help. He tells Ben to take her as he walks over to Bernie's truck. Chin's been checking it out but there's nothing to be found. Opening the glove box, McGarrett finds the remote but tosses it aside. Danno runs up to McGarrett with a map found in Bernie's pocket and they take off back to Park Headquarters. They compare the map with the aerial photos and Danno is sure the 'x' is where Bernie stopped when he went to the rift. He wants to take an Army demolition team to the rift to look for the detonator but McGarrett is hesitant until Danno explains in less than an hour the works is going up anyway. McGarrett okays it calling the governor as Danno takes off.
Outside, Danno takes the team to the rift where they'll try to find and disarm the detonator. The conversation with governor goes as expected even though neither is happy about the situation. The governor must order an evacuation of Hilo and McGarrett busies himself with the television remote realizing that's the trigger! He runs out to the running helicopter but not before pinpointing the impound lot. He asks the pilot to take him to police headquarters but there's no place close to land there. McGarrett then remembers the remote he tossed into the convertible! He tells the pilot to forget about police headquarters and they'll go to Bernie's house instead.
Danno and the Army demolition team arrive at the rift and they begin searching for the detonator finding it fairly quickly in the ditch. Meanwhile, the helicopter lands near Bernie's house where McGarrett runs for the remote. They take off again heading for the rift. As they come in, Chin yells to Danno to back off after he says the thing is "double wired". After landing, McGarrett runs to Chin yelling to Danno for him and the Army guys to back off, which they do. McGarrett hits the remote, stopping the detonator. He then requests a patch to the governor.
This plot summary Copyright Bobbi Baker ©2020. No reproduction of any kind without permission.