MacGyver’s friend and insurance investigator Danny Barrett calls him to a crime scene to tell him that jewels have been stolen, and it’s part of a series of heists. Danny knows who is responsible but can’t touch him because he’s a cultural attaché with the nation of Kanubia and they can’t touch him because of diplomatic immunity. Danny wants to collect the reward and not bring in the police, and needs MacGyver’s computer expertise to hack the embassy’s files. Danny has determined the diplomat stored the necessary info on the computer. They’re interrupted when a van drives by and runs over Danny, and then flees the scene. As Danny lies dying, he whispers the password “Blue Ice” to his friend.
Later, Pete and MacGyver go the funeral home to pay their respects and see Danny’s sister Nikki Carpenter. MacGyver talks about how Danny was in his senior class and everyone loved him. He vows to find the killer, the diamond thief, but Pete warns him to walk away for a couple of days. MacGyver refuses to accept that and gets Pete to help. Pete learns that the cultural attaché, Amir Sumal, is hosting a reception for art patrons at the consulate and no one can get in without an invitation. Nikki arrives and manages to steal an invitation from a guest to get in. MacGyver sneaks over the fence and make a grappling hook out of a garden hose and a rake head. He climbs up to the second floor and enters Sumal’s office where his computer is located.
Inside, Nikki spots Sumal and discovers that the second floor is restricted. She dresses as a waitress and slips upstairs. Meanwhile, MacGyver accesses Sumal’s computer. He gets in using the password but is forced to slip outside when he hears someone coming in: Nikki. She gets on the computer but MacGyver comes in and grabs her. She knocks him down, pulls a gun, and demands to know who he is. A security guard comes in and MacGyver hastily grabs Nikki and starts kissing her. He claims that Nikki is her fiancé but the security guard doesn’t believe them. He calls for backup and MacGyver distracts him long enough for Nikki to knock him out.
MacGyver gets back into the computer and downloads the information via modem. Another security guard arrives and they shut down the computer and then leave the way MacGyver came in. Nikki steals a car and leaves and MacGyver pays the valet to get her car and follows her to Danny’s office. He figures she’s a fellow insurance investigator and accesses the information he sent from the embassy. MacGyver discovers that it’s scrambled and Nikki says that she has a decoder disk in her car that can descramble it. MacGyver takes the paper and goes outside only to discover that Nikki has called the police and claimed he stole the car. Nikki drives away with the information.
Later, Pete bails MacGyver and MacGyver returns to the houseboat. He descrambles the information and learns it refers to diamond grades. Nikki slips in but MacGyver spots her. She apologizes for getting him into trouble but he figures that she couldn’t break the code. Nikki explains that Danny was her brother and she had no idea who MacGyver was. She worked in a Senate subcommittee after graduating from law school, but left the position and came to see Danny. Nikki tried to warn her brother he was in over his head but he insisted on breaking the case and showing everyone he was important. MacGyver offers to team up with her so they can get revenge on Sumal and Nikki agrees.
MacGyver and Nikki take the decrypted file to Pete and insist it’s a list of the diamonds Sumal has stolen. MacGyver figures that the diamonds are still at the embassy. Pete warns that they can’t touch Sumal and the best they can do is ship him home if they catch him with the diamonds. MacGyver suggests they need some diamonds and they steal them from the code room at the embassy where Sumal is saving them. When MacGyver learns that Sumal plays squash, he figures the thief carries the key to the diamonds with him and they need to go to the racquet club and make a duplicate of the key. Now all they need is bait.
Nikki bribes a maitre’d at Sumal’s restaurant to claim he’s at her table. She takes the table and then allows Sumal to stay. Nikki claims that she’s part of a family owning a large diamond, one of twelve, and her brother plays squash. Sumal invites her on a date but when Nikki says she’s busy, he suggests he go with her and they have lunch with him. As they leave, a man at a table covertly watches them.
Nikki takes Sumal to an office building where Pete and MacGyver already have a team set up pretending to be a diamond exchange. She introduces MacGyver as her brother and shows the diamond to Pete. He “confirms” it’s a real diamond and locks it in a vault for safekeeping. Nikki notices there are two shipments of diamonds ready to go and Pete invites them in to take a look. As they leave, Sumal gets MacGyver to accept a squash match. The same man from the restaurant is watching them.
As MacGyver and Sumal change clothing and meet with Nikki, MacGyver secretly tells Nikki that he was unable to get the key. He sends her to the men’s locker room to get it while MacGyver plays Sumal at squash. She borrows a bar of soap from a man taking a show and makes an imprint while MacGyver defeats Sumal. Back at the houseboat, MacGyver makes a duplicate key and damns her with faint praise. She’s got herself invited to the ambassador’s reception but MacGyver has a better idea.
Nikki arrives at the party for the reception and notices the same man following her. The valets park her car and MacGyver emerges from the trunk. He sneaks into the embassy as a delivery man and enters the dumbwaiter. Inside, Sumal explains to his superior, Ambassador Vulnay, why it’s important to have the reception. He shows Nikki the embassy art collection and she comments that she figures the man following them was one of Sumal’s men. He has no idea who it was and checks the camera. While Sumal’s occupied, Nikki takes one of the paintings.
MacGyver uses the duplicate key to get into the code room just before a security guard spots him. The safe has a six-pad keypad and MacGyver uses pencil shavings to determine which three keys open the safe. He runs the combinations until he gets the safe open. MacGyver takes the stolen diamonds and leaves.
Sumal has his men arrest Nikki’s follower while Nikki escorts Sumal out to her car. She passionately thanks him while MacGyver slips back into the trunk, and then she drives away.
Sumal interrogates the man following Nikki, who is a private investigator named Charles Keach. He claims that Nikki is a jewel thief that is setting Sumal up so she can steal a painting from him. Sumal checks the art gallery and realizes the painting is missing.
Nikki meets MacGyver at the houseboat and shows him an electronic device. She wonders if it’ll work. They’re interrupted when Sumal and his guard arrive and demand the painting. Nikki turns it over and Sumal discovers they have blueprints to the diamond exchange. He figures that she and MacGyver are planning to rob the exchange and prepares to kill them. When Sumal prepares to kill them, MacGyver says that they already have everything ready and the diamonds are being shipped tomorrow. Sumal needs them to pull off the robbery.
They go to the exchange and Nikki fakes a mugging to get the security guard to let her in. She then shoots him and gets him out of the way, and then lets MacGyver, Sumal, and Sumal’s guard come in. They take an acetylene torch up to the exchange, enter the vault’s antechamber, and burn through the door. Once MacGyver and Nikki put the diamonds in an attaché case, Sumal draws his gun and breaks the valve off of the acetylene tank, and then locks the antechamber door.
Once they’re alone, MacGyver unscrews a valve from one tank and attaches it to the open tank to seal it. He then opens the door and they head downstairs. Sumal and his guard leaves, and the “dead” guard revives. Keach arrives and drives MacGyver and Nikki to the embassy.
Sumal arrives at the embassy to find Pete and Vulnay waiting. Pete tells Sumal who he really is and tells Vulnay to check the attaché case that has the diamonds. MacGyver, Nikki, and Keach arrive and slip over the fence. Meanwhile, Vulnay refuses to allow the search. MacGyver uses the electronic remote to open the briefcase. Vulnay has Sumal arrested and taken away.