MacGyver visits Western Tech, his alma mater, to judge the annual Fizzics Follies competition. One of the four finalists is David, the son of his mentor, Nobel laureate Professor Ryman.
MacGyver visits the Physics Hall of Fame, where past winners of the contest are enshrined. His mentor was the first winner of the contest and MacGyver won 15 years later. They discuss old times and life choices before Ryman invites him to see the "next generation" in action in the physics lab. When they enter, among other things, David is having problems with a gas leak in an experiment. David complains that he doesn't have the materials to plug the leak. His father humiliates him by quickly plugging it with chewing gum before unleashing some withering public criticism. MacGyver tries to tell the professor he's putting too much pressure on David but finds him unsympathetic.
David promises to win his father's respect by winning the barricade contest. He shows off his setup to his girlfriend, Janet. It's a piston pressed against the door by a remote controlled garage door opener, along with a scale model visible through the room's peephole that shows the reverse action. When the real door is unblocked, the model door is blocked and vice versa. Unfortunately, one of his competitors, Geoffrey, saw them headed for the room and listened in with a parabolic microphone. When Janet finds stimulants in David's room, she argues with him and runs off.
The next day, the contest begins. Aaron has 12 deadbolt locks on his door. Some are open and some locked, the trick being to find the right combination. Hillary has a scale balanced with glasses of chablis and water. Tilting it either way will complete a circuit and open the door. David describes his challenge. Geoffrey shows his door has an electric time-lock. The contest begins.
Geoffrey uses iron filings and a magnet to see which deadbolts are extended. David uses a frequency generator and a loudspeaker to shatter the glass of chablis and tip the scale. Geoffrey and David are the finalists. David hooks up a frequency converter to the AC line to increase the speed of the time-lock. Geoffrey figures out the frequency and pretends to have found the fake solution. Just before the time-lock disengages, Geoffrey "figures out" it's an illusion and opens David's door. David feels disgraced and runs off. As the students head off for drinks, MacGyver looks inside the room and is impressed by David's ingenuity.
At the celebration, MacGyver explains David's problems to the professor then challenges Geoffrey to explain how he figured out the solution. Geoffrey slips up by mentioning the model inside the room, which MacGyver says he couldn't have possibly known about since he never went inside. Everybody knows Geoffrey has cheated. The professor and MacGyver head out to find David.
David is drinking heavily and downing handfuls of pills in the physics lab. He's created the ultimate barricade, wiring the entire lab and building a bomb. Ryman and MacGyver head to the lab after Janet tells them where David is. The danger is grave because the nuclear physics lab above Ryman's holds plutonium.
They find the doors of the lab on the floor and the entrance wired with high-voltage arc generators triggered by a motion detector. While Ryman keeps David talking, MacGyver scours the building for a way in. He finds a janitor's closet, where he fills spray bottles with acetic acid and ammonia. He returns as David passes out. Spraying the two liquids, MacGyver produces a cloud that blinds the motion detector. They go in and find the bomb. There's no time for the bomb squad, so they try to disarm it themselves. But the mercury switch is too far inside to be frozen with liquid nitrogen and the casing can't be opened without detonating it. They try to move the bomb to the elevator so it can explode in the basement but get trapped in the elevator with the bomb. With only a minute left, MacGyver strips wires from the elevator control panel and arcs them beneath the switch to destroy it before time runs out.
Afterward, David is taken out for medical treatment, and Professor Ryman assures his son that he'll be there as long as it takes.