MacGyver, suffering from a bad cold, goes to the grocery store to try and find the ingredients for an old home remedy. Two hoods break in and rob the store and MacGyver makes an improvised tear gas bomb with spices, baking soda, vinegar, and a hot water bottle. He punctures the bag and sprays it into one hood's face and an old lady takes out the other thug. The first hood makes a run for it and MacGyver brings him down by throwing a can. Everyone in the store applauds.
Later at the Phoenix Foundation, MacGyver checks in to try to find the books he needs to come up with a cold cure. Nikki comes in and Pete informs MacGyver that the board has voted Nikki on as a member. They still disagree about their respective approaches. Pete informs MacGyver that there is a clause in Nikki's contract that allows her to work alone except when absolutely necessary. Pete tells them both to get out and MacGyver warns Nikki that he can get cranky sometime.
At the Dunbar Postal Station, a man runs around a corner and bumps into Nikki, knocking her down. He grabs her wallet and leaps into a nearby car and drives away. Inside the post office, a bomb is ticking. Nikki assumes the man was a mugger, gathers her packages and gets into her car... and the station blows up a few minutes later.
Later, the man with Nikki's wallet, Erik Dunlap, meets at a distribution company where his employer, Major, berates him for his carelessness and warns that their comrade Marcus' freedom is at stake. Erik insists that he didn't sign on to deliver bombs and he's merely a supplier, but Major warns that he's in as deep as the rest of them. The third man, Juice is working on more bombs. Erik finally gives in but notes they should be grateful. Major examines Nikki's wallet and tells Erik to dispose of Nikki, a witness to the attack.
Nikki calls the police and tells them about the theft. She's watching her neighbor's dog, which is eating her food. The officer says she has to come in and Nikki has no choice but to leave. Erik is outside her apartment watching her as she goes out and takes the dog, Bunky, with her. He pulls out and tries to run her down, and she jumps into the car just in time.
MacGyver is practicing a home cure at his houseboat when Nikki arrives with Bunky to tell him what happened. The police can't do anything and Nikki doesn't know of anyone in her past that might be coming for her. She doesn't want to bother Pete about it and tells MacGyver to forget it.
MacGyver goes to the Foundation where Pete is having everyone work on a case involving a terrorist attack on a cruise line ship. The person responsible was a terrorist, Marcus, and his people blew up a post office that afternoon and are threatening to blow up an entire city block if the authorities don't release Marcus. Pete tells MacGyver to go home while they find Major, Marcus' associate, who slipped into the country with a bomb expert. MacGyver asks Pete if he can see Nikki's dossier to find out who tried to kill her. Pete agrees to let MacGyver look at the file, although he warns him that the information is confidential. The information reveals that she's widowed after her husband Adam died four years ago in a car bombing.
Nikki is taking a bath when Bunky hears someone unlock the door. He barks as Erik enters the apartment but Nikki ignores him. Erik turns off the lights and prepares to garrote Nikki. She comes to investigate and Erik attacks her. MacGyver arrives and hears the noise, breaks in, and knocks Erik to the ground. The two struggle and MacGyver accidentally knocks Erik out a window to the ground below. The intruder runs away and MacGyver makes sure that Nikki is safe.
MacGyver takes Nikki to his houseboat and insists that she stay there until they get things figured out. He figures that Erik wasn't a professional and isn't connected with any of the Mafia families she investigated with the Senate. Nikki realizes that he read her file and snaps at him. She insists she handle it at her own and MacGyver figures that she thinks she's jinxed and blames herself for Adam's death. The mob tried to kill her and got her husband instead. She breaks down crying and MacGyver holds her.
The next day they go back to Nikki's apartment. She still refuses to let MacGyver handle it. He looks around the apartment and finds a photo of Nikki and Adam. He also finds the cable that Erik used to try and kill her. It's asbestos wiring, the same type used with explosives. MacGyver realizes Nikki was mugged near the postal station and figures that she can identify the man. They go back to the Foundation and use an identikit to put together a drawing of Erik. Pete has traced the wire to a stolen inventory at an explosives plant, Webber Pyrotechnics, and an insider was involved. MacGyver and Nikki go to the plant and Nikki spots Erik in a truck. She gets a gun and prepares to capture him, but MacGyver suggests they follow him. He slips over to Erik's truck and attaches a can of paint to the underside. He then punctures it to make a slow leak. Meanwhile, Erik collects the last delivery of wiring from his inside man and leaves. MacGyver and Nikki follow him.
Major and Juice are making a fake postal truck and realize that Marcus hasn't been released. Erik arrives with the final delivery and Major notices the paint and realizes that Erik's been followed. He pulls out a gun and prepares to leave his pursuers something to find.
MacGyver and Nikki arrive at the distribution company and call Pete. He confirms that Erik is a lowlife who handles shady deals. MacGyver goes in alone and finds Erik dead at his desk. Outside, Nikki gets impatient and goes inside. MacGyver checks out Erik's body and steps on a pressure plate attached to explosives. He spots Nikki and tells her to get out. She retreats to a safe distance and MacGyver uses a table and the chair Erik is sitting on to hold down the pressure plate. MacGyver steps off the plate and nothing happens... until Erik's corpse shifts. MacGyver gets into a cabinet as the explosives go off and it's blown clear by the blast. Nikki makes sure he's safe as Pete and the police arrive. MacGyver and Nikki examine Juice's workbench and find photos of their targets, including the next one: City Hall. They also find stencils for a U.S. postal truck and realize how the terrorist are going to get the bomb in.
Major and Juice, dressed as postal workers, pull up in the fake postal truck. Juice activates the bomb while Major notices an approaching police car. They try to walk away but the police arrive and order them to surrender. MacGyver, Pete, and Nikki arrive while Major and Juice inform them that there's no way to disarm the bomb. MacGyver admits that there's nothing he can do and they have less than ten minutes to move the truck. He has no choice but to drive it off the 2nd Street pier. MacGyver drives it there with the police providing escort. However, they don't have enough time and come to a truck blocking off the street. MacGyver drives down a hill to the next street but is stopped by a road construction team. Another truck pulls up behind him, cutting him off.
With less than five minutes left, MacGyver convinces the cement truck driver to fill the truck with cement. The seconds run down and the bomb blows up... safely contained by the concrete. MacGyver admits he wasn't sure what his Plan B would be, and Pete catches his cold.