MacGyver catches a bad cold and goes to the local grocery store to buy the ingredients for a cure. Two hoods in hockey masks break in and rob the place. Thinking quickly, MacGyver mixes cayenne pepper, garlic powder, baking soda, and vinegar in a hot water bottle and quickly corks it. He then goes up to the front and uses his Swiss Army knife to puncture it, spraying the blinding mix into one hood's eyes. An old woman clubs the second man unconscious. The first hood tries to run for it and MacGyver brings him down with a thrown can.
MacGyver goes to the Foundation to find a book with cold cures and discovers that Nikki has been voted in as a Foundation member. They argue about his improvisations over her careful planning. However, Pete assures them that per Nikki's contract she can work alone except when absolutely necessary, and tells them both to get out.
Later, Nikki is shopping and walks by a postal station. A man runs out and knocks her over. He grabs her wallet and then jumps into a nearby car that drives away. Nikki picks up her packages and drives away. A minute later, the postal station blows up.
Nikki's attacker, Erik Dunlap, goes to his distribution company. He's working for Major, a terrorist, who insists that they need to get their comrade Marcus free. Erik insists he's an explosives supplier, not a field operative, but Major tells him that he's in just as deep as himself and his bomb expert, Juice. Erik agrees to help and Major tells him to dispose of Nikki before she identifies Dunlap to someone.
Nikki is watching her neighbor's dog as she calls the police. The officer tells her to come in and make a report. As Nikki leaves with the dog, Bunky, Erik tries to run her over and just misses. Nikki talks to the police and then goes to see MacGyver at his houseboat. She explains the police can't do anything and she doesn't know of anyone who'd want to kill her. She reconsiders and tells MacGyver to drop the entire matter.
The next day, MacGyver goes to the Foundation and interrupts Pete, who is leading a task force to track down the persons behind the postal station bombing. The terrorists responsible have informed the city that the first explosion was a warning, and if Marcus isn't released then they'll blow up a city block. Pete assures MacGyver they have the situation under control and he should go home and get some rest. He lets MacGyver see Nikki's file and warns that it's confidential. MacGyver checks the computer files and discovers that Nikki's husband Adam died in a car bombing four years ago in Washington, D.C.
Nikki is relaxing at home in the bath when Bunky barks at an intruder. Erik breaks into the apartment and turns off the lights. When Nikki goes to investigate, Erik tries to strangle her with a piece of wiring. She struggles and MacGyver arrives outside. Hearing the noise, he breaks in and Erik attacks him. Erik is knocked out the window and runs away while MacGyver makes sure that Nikki is safe.
MacGyver takes Nikki to his houseboat for safekeeping and concludes that Erik wasn't a professional. He mentions the Mafia families that Nikki investigated when she was in Washington and she realizes MacGyver has been looking through her confidential files. He tells her that she can't go on blaming herself for her husband's death and Nikki explains that the Mafia came after her and killed her husband by accident. She cries and MacGyver comforts her.
The next day the pair goes back to Nikki's apartment. MacGyver finds the garrote wire and realizes it's asbestos wiring used with explosives. When he learns that Nikki was mugged near the postal station that blew up, he figures the terrorists are trying to eliminate the only witness. They go to the Foundation and put together an Identikit sketch of Erik. Pete traces the wiring to Webber Pyrotechnics, which reported an insider theft of explosives.
Nikki and MacGyver go to the company and spot Erik making a pickup from his inside man. MacGyver slips under Erik's truck and hangs a can of paint from the undercarriage, and then punctures it with his knife. They then follow the truck from a distance by using the traces of yellow paint. Erik returns to his distribution company, where Juice and Major are using stencils to paint a fake postal truck. Major notices the paint trail and realizes that someone is following Erik. He pulls out a gun while saying that he prepares to leave something for Erik's pursuers.
MacGyver and Nikki arrive at the plant and call Pete. Pete confirms that Erik is a known supplier to the underworld. MacGyver insists on going in alone and finds Erik in his office, perched in an office chair and dead. He moves in to check the body and steps on a pressure plate attached to plastic explosive. Nikki comes in and MacGyver tells her to stay back. She retreats to a safe distance while MacGyver balances Erik's corpse and the swivel chair on the pressure plate. He then steps off but Erik's corpse shifts. MacGyver dives into a cabinet and the explosives blow it clear. Nikki gets him out as Pete arrives with the police. They go through the terrorists' workbench and find photos of their target. The next target is City Hall. They also find the stencils and realize the terrorists have the bomb in a fake postal truck.
Major and Juice pull the fake postal truck up to City Hall and activate the bomb. The police arrive and arrest them. MacGyver and the others arrive and Juice boasts that the bomb can't be disarmed and they have only ten minutes left before the entire city block is destroyed. MacGyver gets into the truck and drives it for the nearest pier while Pete and Nikki follow in a police car. Construction is against them and a construction crew blocking traffic as they pour concrete finally brings MacGyver to a halt.
With only a few minutes remaining, MacGyver tells the cement truck driver that they have a bomb and has him pour the concrete into the back of the postal truck. MacGyver gets clear as concrete covers the entire bomb. It detonates and the concrete smothers the blast. MacGyver admits that if there hadn't been a concrete mixer, he would have come up with something else: he just isn't sure what. And Pete catches MacGyver's cold.