At the car wash, MacGyver is getting his father's classic truck washed and stops to chat with the worker, Chauncey. Chauncey dismisses it as a piece of junk but is impressed when a woman finds the truck, and MacGyver, attractive.
Sofia Parker is walking her dog Frog at Expo Park and stops to talk to an old woman. Frog runs off after another dog and into the park. Sofia slips through the gate after him, unaware that Deegan, March, and Reynolds are meeting inside. Deegan has a letter from their fourth man, Simms, who says that each one of them has a piece of a plastic map that will lead them to the spot in the park where the Black Corsage is hidden. Deegan and March make sure that Reynolds has his piece and then draw their guns. Reynolds runs and Deegan wounds him, but the man manages to get away, stumbling into Sofia. He puts his map piece into her pocket and runs away, while Sofia gets out of the park but is forced to leave Frog behind, leashed to the gate. Reynolds collapses and Deegan and March search him. When they don't find his map piece, they realize Sofia has it.
Sofia goes to a phone call and places an emergency call to Pete's private line at the Phoenix Foundation. She identifies herself as Dolphin and asks for assistance. However, Deegan arrives and fires at her. Sofia drops her purse and runs away from March. Deegan checks the phone receiver and hears Pete at the other end. Once Pete hangs up, Deegan gets Sofia's purse. He then calls the operator and, pretending to be a homicide cop named Murphy, learns that Sofia called the Phoenix Foundation.
While Sofia manages to escape, Frog manages to pull free of his collar.
The police are called in to investigate Reynolds death. MacGyver and Pete go there, and Pete warns his friend that because Sofia was a Bulgarian defector in the Foundation's relocation program, they can't notify the police of what's really going on.
Outside, a man examines Frog's abandoned collar and gets Sofia's address from the dog tags.
Deegan and March get Sofia's address from her purse. They don't find her there, although Deegan finds a photo of her with MacGyver at his houseboat. They also find a Foundation ID tag identifying Sofia as a lab technician. Realizing where she works, Deegan and March go the laboratory and Deegan talks to the guard. Sofia goes there for safety but sees Deegan and is forced to leave.
MacGyver tries to find Sofia at her house and finds Frog has already returned there. Going inside, the man in the black coat ambushes MacGyver, mistaking him for Deegan. He identifies himself as Frank Colton, bounty hunter Jesse Colton's brother and a member of the same profession. He frees MacGyver and explains that Jesse is in Hawaii and Frank is working his brother's cases. They verbally spar with neither wanting to tell the other anything. MacGyver prepares to leave on his own but Frank mentions the map and MacGyver has no choice but to take him along.
March goes to a telephone switching station and taps into Pete's line. He updates Deegan on his progress, and warns that Pete is involved in a high-security program.
MacGyver and Frank go to the lab and talk to the security guard, who notes that Deegan was there. MacGyver checks in with Pete, who has checked his contacts and is confident that the Bulgarians aren't trying to get Sofia back. MacGyver stops at an outdoor diner and finally tells Frank what's going on. He explains that Sofia's father wrote a pro-democracy book. After he died under mysterious circumstances, Sofia tried to publish the book and MacGyver had to get her out of the country. The Foundation then set her up with a new identity.
In exchange, Frank explains that four thieves penetrated a computer security system to steal the Black Corsage, a necklace with a rare black pearl setting. Simms was captured and the other three men disappeared. The Corsage was never found and Simms was killed in prison. The insurance company learned that Simms hid the Corsage without telling his partners, and then made a map and divided it into three pieces to make sure they didn't betray him. Frank went to Expo Park and found Reynolds, and figures he gave his piece to Sofia. MacGyver finally gets him to admit that he's working for the insurance company's reward money.
Sofia goes to the train station to call Pete from a pay phone. As she looks for change in her pockets, she finds Reynolds' piece of the map. She makes contact with Pete, who tells her to meet MacGyver at a diner. Deegan and March, listening in on the phone tap, head for the diner. As she leaves the station, Sofia hides the map piece in a promotional cardboard cutout of the Statue of Liberty.
Pete calls MacGyver and tells him that Sofia's at the diner. Meanwhile, Deegan arrives at the just after Sofia and narrowly misses seeing her. She spots him and slips out the back, snagging her dress on a nail. MacGyver has Frank stay with Frog while he goes inside, brushing past Deegan. The crook recognizes him from Sofia's photo. MacGyver talks to the waitress, who directs him toward the back. Frank and Frog meet him back there and the dog finds the bit of Sofia's dress. Frog starts following her trail and MacGyver and Frank follow him, while Deegan and March follow them.
Sofia takes refuge in an empty fish processing plant. Frog leads the men to the plant and finds Sofia. Frank and MacGyver find her, but Deegan and March get the drop on them. When Frog attacks March, Frank tries to intervene and Deegan shoots him in the shoulder. The crooks then demand that Sofia give them the map piece. When she refuses, they tie up MacGyver and Frank and put them into a conveyer belt leading to a fish grinder. She gives in and tells Deegan where the map piece is, and the crooks turn on the machinery and leave.
As the men head toward the grinder, MacGyver tries to get Frog to bring him a hose so they can spray the circuit box and shut down the belt. Frog ignores him and Frank as well when the bounty hunter tries to get the dog to bring him a knife. However, Frog hits a lever, opening a diversion channel on the conveyer belt and dumping the men into a bin filled with dead fish. MacGyver cuts them free with fish teeth. They figure that the men are going back to Expo Park to get the Corsage.
Sofia gets the map piece for the crooks. When they put the transparency together with their pieces, they realize the Corsage is hidden in the Expo Park carousel. MacGyver, Frank, and Frog get there first. They hide and wait while Deegan and March go to the carousel. The necklace is hidden in plain sight on a gypsy mannequin at the center of the carousel. While March gets the Corsage, MacGyver and Frank slip beneath the carousel platform. Deegan prepares to kill his partner but MacGyver turns on the carousel and Frank knocks March out. MacGyver grabs the Corsage and runs, drawing Deegan's fire so Sofia can escape.
MacGyver manages to avoid Deegan and enters an amusement arcade. Searching, he finds a booth with a shooting gallery. MacGyver attaches the cable from one of the guns to the Corsage and leaves it in plain sight, then rigs the canopy with a pole and cable. Finally, he opens the outside door, leaves his shirt outside, and sets off the fire alarm. Deegan comes running, spots the Corsage, and tries to pick it off. That releases the pole, dropping the canopy on him and giving MacGyver enough time to disarm him. Frank arrives to capture the crook.
Later, Pete, MacGyver, and Frank are waiting as Sofia packs her belongings so that she can relocate. March gave state's evidence against Deegan and the two are going to jail. Frank has collected his reward from the insurance company and is satisfied. However, Sofia has to leave Frog behind as she goes into her new identity. Once she's gone, MacGyver and Pete discuss whether Frog will have to go to the pound. Frank gives in and takes the dog as his new pet.