As a child in 1963, MacGyver and three other boys, Jesse, Neil, and Chuck, swear to return in 25 years to dig up a time capsule they've made out of a lunch box. They bury the box .
In the present, MacGyver returns to his hometown of Mission City to follow up on his promise, believing he has to keep it no matter how much it hurts. He pulls up to a home and remembers how he and his friends gathered enough money to buy a gun.
At an outdoor basketball court, four drug dealers pull up to a basketball court and one of the players, Sean, takes off running. The gang cut him off and their leader, Spider, wants to know where Sean has been for the last two days. Sean insists he's out of it but Spider warns that he only gets two chances. They're interrupted when Sean's friend Danny arrives, gets up on Spider's car, and threatens to break the windshield with a rock. Danny tells Spider to stay away with his friend. One of Spider's thugs, Watts, pulls a gun and Danny drops the rock, shattering the windshield. He runs and Danny and the others chase after him, but a police car goes by and they're forced to give up the chase.
Once they get clear, Danny wants to know what's going on and Sean insists he's not doing drugs. Danny says he's not going to bail his friend out any more and starts to walk away. Sean stops him, insisting Danny is the only friend he's got. Danny agrees to stand by him.
MacGyver arrives at his friend Chuck's gun store. He's surprised that MacGyver still wants to keep a kid's promise, and MacGyver says he'll go alone if he has to, but he'd like Chuck and Neil there. Chuck finishes trying to sell a gun and MacGyver notices the customer's son playing with a handgun. He remembers struggling with one of his friends over a gun as a child. Once Chuck finishes selling a rifle, MacGyver calls him on selling guns but Chuck insists that if he didn't, someone else would. He tries to distract MacGyver, but MacGyver insists on doing what he came to do. Danny, Chuck's son, arrives with Sean, Neil's son. They talk briefly with MacGyver and leave, and Chuck admits he never told Danny what happened when he was a child and doesn't want Danny to know. MacGyver insists it was his fault as well and Chuck agrees to go through with their promise if MacGyver can convince Neil to go along with them.
MacGyver goes to the police station to see Neil. He helps a desk sergeant fix his typewriter and the sergeant remembers MacGyver as a boy.
Spider arms his local gang members, J.D., Meat, and Watts, and tells them that if they want to own the town, they're going to have to do things his way.
MacGyver finds Neil, who admits that he wasn't sure if he can get up the nerve to go with the others. MacGyver insists he has to.
Spider and his gang watch Chuck's shop until Danny comes out. They drive by and Meat opens fire with a shotgun, and Danny dives for cover just in time.
Neil and MacGyver arrive and Neil describes how Spider came into town from Los Angeles and set up crack deals in Mission City. Danny denies knowing anything about Spider and goes inside with Sean to clean up. Danny warns Sean that he needs to tell Neil what's going on. Sean has heard that Spider's contact is coming in with a major shipment and they should tip off the cops. He suggests that Danny hide out at Bell Lake and tell his dad that he's going on a fishing trip. Danny agrees and Sean tells him to meet him at the pump house near the abandoned state hospital in an hour.
MacGyver goes to get them and sees Danny taking one of his father's handguns. He remembers picking up a handgun as a child. He runs in and takes the gun from Danny and demands answers. Danny explains that a friend got in trouble with Spider and he needs a gun, but doesn't think it'll turn to killing. MacGyver realizes Sean is involved and refuses to let Danny handle it on his own. Danny knocks a shelf over on him, grabs the gun, and runs out the back. When Neil and Chuck come in, MacGyver explains what happened and that Sean is involved.
The police track down Meat and J.D. and arrest them for the driveby shooting. Watts prepares to walk but Spider warns him that his people will hunt him down if the cops don't catch him. Watts agrees to stay and Spider figures once they kill Danny, the only witness, they're can use Sean's drug habit to keep a hold on him.
Danny arrives at the pump house by the state hospital and loads the gun, dropping some of the bullets. Sean prepares to leave his house. Spider and Watts capture him and Spider offers Sean a free bottle of crack if he'll give up Danny. Sean tries to refuse but soon gives in.
MacGyver goes to the school and finds Sean, high on crack. He admits he told Spider where Danny is and tells MacGyver that his friend is at the pump house. MacGyver tells Sean to tell his father what's going and then heads for the state hospital himself.
Danny sees Spider and Watts coming and runs to the abandoned hospital where he crawls in through a window. Running through some oil, he comes up from the basement to the upper floors. Spider and Watts follow, spotting the oily footprints. MacGyver arrives at the pump house and finds the bullets, and remembers back to his childhood when he and his friends loaded the gun they acquired.
In the hospital, Spider and Watts hear Danny up above on the third floor and go in pursuit. MacGyver enters the hospital while up above, Spider and Watts corner Danny. They fire at him and MacGyver, hearing the gunshots remembers when he fired a gun with the others when he was a kid. The fourth friend, Jesse, refused to participate but Chuck and Neil were eager to shoot.
Spider and Watts close in on Danny's position, unaware he's hiding to the side. When they go into an outer room, he locks the door behind them but Watts open fire with his shotgun.
MacGyver, hearing the shot, remembers that Neil decided to shoot at a bird. MacGyver tried to stop him and knocked the gun out of his hand.
MacGyver spots Danny as he runs down the stairs. Danny slips on some of his dropped bullets and falls, shooting himself. MacGyver remembers back to the gun going off when it hit the ground, shooting Jesse by accident.
MacGyver gets Danny up and takes him into an old treatment room. As he tries to help Danny, he remembers Neil and Chuck running off as he tried to help Jesse. MacGyver goes through the old medical equipment and finds some bandages to try and stop the bleeding. Upstairs, Spider and Watts break down the door and split up to search the hospital.
As Danny asks MacGyver not to leave him, MacGyver remembers Jesse saying the same thing to him. He finds some phenolphthalein solution and mixes it with drain cleaner to create a blood-like substance.
In the past, MacGyver strips the wheels from his bike and puts the metal struts together to make a crude wheeled travois.
Backtracking, Watts spots what appears to be Danny's blood and follows the trail. He's unaware it's MacGyver using the fake blood. MacGyver puts a fake bloody handprint on the door into a refrigerator vault and then waits inside. When Watts checks out the door, MacGyver knocks him in and locks the door. However, Spider gets the drop on him and demands to know who he is. MacGyver tries to feign ignorance and claims he works there but Spider doesn't believe him. He forces MacGyver back to the treatment room and spots the blood, but Danny has hidden himself. As they go further in, MacGyver spots Danny hiding behind a screen. When Danny collapses, MacGyver uses the distraction to grab a gurney and ram Spider through a glass window, knocking him out.
In the past, MacGyver gets Jesse to a nearby road and finally manages to flag down a car to call an ambulance.
With time running out, MacGyver gets Danny onto the gurney and wheels him to the outside door. He uses a food cart to smash through the door and gets Danny outside just as Chuck, Neil, and Sean arrive. MacGyver tries to keep Danny alive until the EMTs arrive. They go to work.
In the past, Jesse is declared dead while MacGyver insists it was an accident.
The EMTs manage to stabilize Danny.
Later, MacGyver, Chuck, and Neil dig up their time capsule. Neil blames himself for missing the signs of his son on drugs, but MacGyver assures him that getting Sean into a treatment program is a good start. Danny will be all right as well. MacGyver opens the time capsule and they open it together. Inside is each one's childhood item: Neil's rubber spider, Chuck's baseball, and MacGyver's homemade non-killing mousetrap. The final item is a photograph Jesse took of the four of them, with a note saying they were the best pals he ever had.