A boxing match is in progress between Joey Kalama (Jerry Summer) , a.k.a. "The Maui Kid," and another boxer named Torilino. Joey gets knocked down and nearly out, but manages to get back up after much encouragement from Phil (Frank deKova), his father. Joey then knocks out Torilino and win the match.
In Joey's dressing room after, Phil suggests going out and celebrating the victory. Danno, who was with Phil and Joey's girlfriend Lois Walker (Jean Hale) at ringside, has to take a rain check. Phil mentions making a reservation for two but Joey wants it for three, including Lois.
Later outside, Joey and Lois are walking when headlights from a car are turned on, blinding them. Two thugs approach and a fight ensues. Joey is badly beaten. After he goes down, the thugs run back to their car and take off. Lois struggles to see who is in the car.
Joey has succumbed to his injuries; his body is taken away in an ambulance. Lois, Phil and Danno are at the scene. McGarrett quickly shows up. He approaches Joey's manager Nat Keller (Jesse White), who is also there. Nat says that everyone loved Joey, a boxer with 15 straight wins, 10 by knockout: "The best fighter I ever handled." McGarrett asks Nat, "A lot of money riding on tonight's fight, Nat?" Nat insists he's only a manager, not a gambler.
Phil tries to get information about the beating from Lois, but she tells him the headlights blinded her and she didn't see anything. Lois says, "He died a winner. That should make you happy." Phil exclaims, grabbing her, "Why you cheap, little tramp!" McGarrett steps in and separates them.
Phil says he has to talk to Keller and Joey's trainer Luther (Charles Lantkin) but McGarrett reminds Phil that this isn't his jurisdiction, Maui. Danno leaves with Phil and Lois, driving them home.
In the locker room, McGarrett speaks to Luther, who says that Joey needed "eight more fights and he was a contender." Luther adds that Joey "had all the moves and more. Something you can't teach a kid. Class, moxie, he had it all." McGarrett wonders if Joey had money problems. Luther says after paying off his manager, trainer, sparring partners, seconds and expenses, "the guy catching all the punches winds up on the short end." Trying to get more information out of Luther, McGarrett mentions his conversation with Keller, who said that he was not a gambler. Luther scoffs, "That's a laugh." He says that Keller owes money to Nick Morgan (Mark Richman), a shady gambler who was also at the match-+.
McGarrett and Danno go to see Morgan. He says Joey's death is "a great loss to boxing." McGarrett wonders, "If Joey was such a good boy, how come you dropped a bundle on Torilino?" Morgan says that he had 10 to 1 on Torilino. When McGarrett questions this, because Joey was likely to win the fight, Morgan points out that Torilino almost knocked Joey out.
At this point, Phil barges in, looking for information. Morgan tells Phil he doesn't believe he can be of any help. McGarrett needles Morgan, suggesting that he could have made a lot more money off the fight than he did. Morgan's attitude is "you win some, you lose some." Pushing further, Danno mentions Nat Keller. Morgan denies knowing him while Danno says that they have heard Morgan is holding some of Keller's markers (IOUs). Morgan calls the information "a bum tip," adding "Managers don't bet on anything. It's in the rule book."
McGarrett asks where Morgan was when Joey got hit. Morgan's alibi is he was playing gin rummy in his car with "the world's most beautiful gin player." Phil totally flies off the handle, grabbing Morgan by the throat, yelling "No more games, Morgan." As Phil screams "He's got to talk," McGarrett gets Danno to take him outside to calm down. Morgan asks McGarrett, "Where does he come off, acting that way?" McGarrett replies, "He just lost his only son." Morgan says, "I'm sorry somebody killed his boy," but tells McGarrett to keep Phil off his back.
Outside, McGarrett is furious at Phil. He points out there is no evidence against Morgan and Phil was ready to throw away 23 years of police service because of his outburst. McGarrett states that Joey's death is just another homicide and if Phil can't accept that, to get out. Phil wonders aloud if McGarrett wants him to turn his badge. McGarrett tells Phil to let Five-O handle it: "It's not your bag." If Phil doesn't back off, McGarrett will bring charges against him. Phil relents as McGarrett promises to find the people responsible. Before they part, Phil brings up Nat Keller, whether he is a gambler as has been rumored. McGarrett tells Phil that he will talk to Keller again.
Later at the Five-O office, Danno tells McGarrett that Keller has disappeared. The desk clerk from Keller's place said that someone else was looking for him. Danno speculates that Keller owed Morgan and Keller went to Joey to throw the fight. Joey refused, he got hit and now Keller is a target for Morgan. McGarrett answers, "Interesting theory. You'll make a good cop one of these days, Danno."
At the now-empty boxing arena, Phil climbs into the ring through the ropes. He flashes back to Joey's win, the chalk outline around his son's body interspersed with pictures of Morgan, Lois, and Nat as the crowd cheers. Phil pulls out his gun to ensure it's loaded.
McGarrett meets Phil graveside after Joey's funeral. Phil tells him how, many years before they moved to Maui, he and Joey came to this cemetery where Joey said that he didn't want his father to come there first, that he wanted them to come there together. Phil further reminisces, recalling that Joey said that he would be "a winner in life." McGarrett tells Phil to stop torturing himself and implores Phil to take a couple of days off. Phil tearfully tells he will.
Back at Five-O, Chin and Kono have nothing to tell McGarrett other than a wide variety of conflicting reports about Keller's whereabouts, Danno says the desk clerk couldn't identify the person looking for Keller from the mug books, and no one is talking about Keller owing Morgan money. Morgan's alibi is confirmed; with a smirk, Danno says Morgan was with a blonde but "couldn't swear to what they were playing." Adding all this up results in a big zero.
Phil tracks Lois to a photo shoot where she is in charge of the models. Angry that she never showed up for Joey's funeral, Phil accuses her of using Joey, that if he wasn't a contender, she wouldn't have given him the right time. Phil says he has no regrets about teaching Joey to be the best in everything he did. Getting to the point, Phil wants to know where Keller is. He knows that Lois was Keller's girl before she met Joey, and maybe Keller never forgave her for leaving. After Phil puts the strong arm again on Lois, she gives him the key to her apartment, which is where Keller is holed up. She tells Phil, "Go ahead and find out why your son was really killed. And then get your gun and blow your brains out."
Phil goes to Lois's place where he finds Nat. He asks why Nat had Joey killed, which Nat says is "crazy." When Phil brings up the money that Nat supposedly owed Morgan, Nat replies, "How could I hurt a kid that could give me the crown?" Phil gives Nat the line from Lois about "blowing your brains out," and Nat again says "That's crazy. Why would Joey want to take a dive?" Phil, startled, says "Who said anything about a dive?" Phil tells Nat, "You thought you had it fixed for Joey to go into the tank. He wouldn't go along, so you had him killed." Nat blurts out, "I had nothing to do with it. It was Morgan." Keller suddenly runs out of the room and attempts to flee by the building's fire escape. When Phil catches up to him and they struggle, Nat falls over the railing to his death 10 stories below.
Keller's body is taken away in an ambulance. Despite a witness who claims Phil pushed Keller from the stairs, McGarrett can't buy Phil as the killer: "You don't get answers out of a dead man."
The Attorney General comes to Five-O headquarters, predictably upset about a "rogue cop" taking the law into his own hands to work out his personal problems because it will undermine public confidence in the police. McGarrett insists that Phil is a "good cop" but a "grieving father." The Attorney General gives McGarrett 24 hours to prove that Phil is innocent.
After the Attorney General leaves, McGarrett calls the team into his office. He briefs them about the 24 hours and asks if anyone knew about Keller being holed up in Lois' place. He then tells them to give out information on Keller and Lois's apartment. McGarrett tells Kono to find Morgan and "don't let him out of your sight."
Phil forces his way into Morgan's residence, but Morgan is not there. Instead, Phil roughs up some tough guy who is watching the place, asking where Morgan is.
The next scene is on Morgan's boat where Morgan meets with Lois, telling her he can make her life very comfortable and says Phil is "Just a cop." Lois corrects him, "He's an avenging angel whose son is not yet cold in his grave." Lois leaves, saying that if Morgan is still in business after everything blows over to ask her again. At this point, we see Kono keeping an eye on Morgan and Phil keeping watch on Kono.
At Lois's apartment, two men named Sugar (Wayne Want) and Elroy (Hal Baylor) break into the place, but Chin and Danno are waiting for them. They take the pair to McGarrett's office to be questioned, but Sugar gives McGarrett a bunch of mouth, saying they don't have to talk. When McGarrett starts floating the idea of a rap for Joey's murder on the two, Elroy looks like he will crack. Sugar says they know nothing about Joey's demise. McGarrett gets Danno to book them for breaking and entering, concealed weapons and murder.
The two thugs are put into a line up for Lois. She denies seeing anything because of the headlights and being panicked. McGarrett and Danno both believe Lois knows something and she finally admits to being scared by both Morgan and Phil. She says of Phil, "I bet anything he'd be here twisting my arm, or " McGarrett presses, "Why would he do that?" Lois says, "Because I killed his son."
In his office, McGarrett asks Lois how she killed Joey. Lois says Joey was supposed to take a dive in the Torilino fight. When that didn't happen, he signed his own death warrant. The dive went against everything Joey knew and how he was raised to be a winner. Lois goes on to explain the money Joey would get fixing the fight was going to be his wedding present to her. When Lois asks McGarrett if the idea of Joey and Lois getting married rocks him, his answer is, "Nothing rocks me anymore, honey." Lois goes on to tell her story of arriving 10 years before and using her assets and all the men along the way. "Then along came Joey, and I could see my jackpot." She then mentions she met with Morgan and McGarrett asks her if it was his money behind the fix. She's not sure because Joey never told her whose money it was. She confirms Nat Keller set up everything.
Morgan is partying with friends on his boat. Kono and Phil watch from across the street. Kono is oblivious to Phil's presence.
Meanwhile, in McGarrett's office, Lois stands by the desk as Chin hauls in Elroy. He and Lois look at one another and, after awhile, she nods to McGarrett. Lois leaves and Elroy says that she is "Joey's dame." McGarrett then asks Chin, "Danny here?" Chin says he's with May typing up Sugar's statement. Elroy says they're bluffing because Sugar doesn't sing for anyone. McGarrett tells Elroy they have a sworn statement from Sugar and he tells Chin to take a copy of the transcript over to the Prosecutor's Office to draw up indictments. Danno walks in and starts reading the transcript. Elroy again says Sugar wouldn't say anything. Finally confronted by what he hears, Elroy yells that all he used was his fists to beat up Joey, not a sap, that he wanted to rough up Joey, but not to hurt him. McGarrett asks him if he wants to make an official statement.
Back at Morgan's boat the party is breaking up. As Morgan's friends leave, Phil runs to his car. This car has a police radio in it, and Phil is able to make a riot call. When dispatch calls to confirm this, Phil responds with bogus information. This is enough to get Kono, who is nearby listening to the police radio, to leave. Phil makes his move toward Morgan, confronting him about what Nat Keller said and the fact that Keller is dead. Morgan takes off on foot.
As the chase leads into the area nearby, Phil pulls his gun. McGarrett and Chin arrive on the scene. Chin notices Kono is gone as McGarrett explains it took half a minute to determine the riot call was a phony "Long enough to make his play." A gunshot is heard. McGarrett runs in the direction Phil and Morgan ran earlier and is close to them when a second shot rings out. Morgan finds himself cornered. He attempts to surrender, but Phil fires again, missing Morgan, who hides. Phil moves in, climbing up on a metal box. McGarrett follows and joins Phil on top of the box. Phil has Morgan dead in his sights with the advantage of being higher, but McGarrett pleads with Phil not to shoot, that Five-O has Morgan "sewed up tight and legal."
Phil says he is going to kill Morgan, but McGarrett tells him, "There's no way you can bring yourself to take the life of that man. You're too good a cop not to know what really happened. You figured it out. You know that Joey sold himself to Morgan. That's what's eating you alive, the thought that maybe you pushed Joey so hard, you drove him to it. That's what you can't stand. That's why you're here with that gun, you're trying to kill yourself. Now, look, Phil, you're too good a cop not to know that what I'm saying is true. Doesn't matter what Morgan did or Keller or Joey. The only thing that matters is that you're a cop. Now, if you blow that, you smear the image of every law-enforcement officer everywhere. You tear down everything we've ever worked for."
Phil puts his gun back in its holster and gets down from the box and cuffs Morgan. McGarrett tells Chin to book Morgan.
Phil still cannot face facts about what happened to his son: "Joey was supposed to lose. It was a fixed fight. But he got off the floor, Steve, didn't he? He got off the floor to win. He could have been a champ." McGarrett straightens him out: "I'm sorry, Phil. He made a crooked deal, then he wouldn't go through with it, and you know it. Now, that's the truth you gotta face up to. That's the truth."