MacGyver is out biking on a Sunday with a tiring Wilt for exercise, who finally gives up. Wilt heads home while MacGyver stops for a paper. A car pulls out of an alleyway and grazes MacGyver's bicycle wheel, knocking him down. The driver backs up and gets out: it's a woman, Lulu, who wants to make sure her car is okay. She insists her boss Izzy wouldn't be happy if she put another dent in it. She explains that Izzy is also her teacher and her best friend, then finally gets around to helping out MacGyver. She puts his bicycle in her trunk and offers him a lift. MacGyver reluctantly agrees and Lulu pulls out. She says she borrowed the car for a party but can't find the invitation, and offers to play some of Izzy's classical violin playing. MacGyver recognizes him Izzy as a famous violinist.
Before dropping MacGyver off at the marina, Lulu stops at a pawnshop and explains that Izzy keeps things there for safe keeping. Lulu finally finds the claim check but discovers the pawnshop is closed. She promises to get MacGyver home as soon as he tells Izzy what happens. She drives to his manor but MacGyver has had enough and decides to walk his damaged bike home. Lulu gives him his paper, kisses him on the lips and then goes inside. Meanwhile, MacGyver finds the 20's party invitation in the paper and reluctantly decides to go back inside. In the house, a thug, Ginko, is playing a violin badly to torture Izzy and then smashes it. Lulu runs in and demands answers. Ginko's boss Tubbs comes in and demands the Amadeus, but Lulu doesn't know what he's talking about. MacGyver hears the commotion and comes inside, and Ginko smashes him over the head with another violin. Lulu finally says she has the Amadeus and will give it to them if they let MacGyver go, and claims MacGyver is her husband. She tells Tubbs she'll make the exchange somewhere public. She spots the invitation in MacGyver's hand and tells Tubbs to meet him there, and the crook leaves with Izzy as a hostage.
Once Tubbs and Ginko are gone, MacGyver insists on knowing what's going on. Lulu isn't eager to involve him but he points out Tubbs wants him there as well. They go to the pawnshop and MacGyver goes to find a phone booth to call the shop's emergency number. A teenager is playing loud music and he can't make himself heard on the phone. Once he turns off the boom box, MacGyver hears an alarm and goes back to the shop, where he discovers Lulu has broke into the shop and found the pawned item: a bag of golf clubs. She explains that Izzy's cousin owns the place and he's fishing in Canada, but he'll understand. They drive off just as the police arrive. After parking in an alley, they find an antique violin in the bag. Lulu explains that Izzy bought it in Salzberg at a flea market and was very excited, and then was troubled the next day. MacGyver also finds a certificate of origin confirming that the violin is a 300-year-old made by Stradivarius that belonged to Amadeus Mozart. Lulu plays it, beautifully, attracting the local street people who applaud.
That night Lulu picks up costumes and heads to the Roaring 20's party. Lulu admits she found the invitation in an ATM and has no idea what it's for. When MacGyver goes to get some apple cider, Lulu switches the Amadeus for a band member's violin. She dances with MacGyver and he assures her they'll get Izzy back. Tubbs and Ginko arrive, wearing 20's police costumes, and pretend to arrest them and put handcuffs on them. Tubbs discovered Lulu has switched violins and Lulu and MacGyver make a break for it. They go into a boiler room but the only way out is a narrow window. MacGyver cranks it open and then they take refuge in a vent. As Tubbs and Ginko search, a rat runs by and MacGyver manages to quiet Lulu before she screams. The crooks spot the window and figure Lulu and MacGyver slipped out that way. However, the rat runs into Lulu's hair and she gives a muffled scream. When Ginko goes to investigate, MacGyver puts the rat out to make him think it made the noise.
Tubbs and Ginko leave and MacGyver and Lulu slip out into the courtyard of a nearby mall. Lulu then tells MacGyver she switched violin. MacGyver is unable to get the handcuffs off and Lulu has to use the bathroom. As they go up the escalator, Lulu asks if MacGyver was ever in love and he admits he was once but never got married. A security guard spots them and MacGyver turns over his driver's license. The security guard lets them go but not before Lulu pickpockets his handcuff key. Once they're free, MacGyver wonders how Tubbs learned about the Amadeus. Lulu explains that an air freight company out by the airport transported Izzy's violins. They hail a taxi and go there, and discover that Ginko filed a damage report and another man asked about it a half-hour ago: Tubbs.
MacGyver and Lulu go to Tubbs' violin store and climb up to the roof. They break in and find Izzy bound and gagged. Tubbs and Ginko come in and capture them. Once MacGyver is tied up, Tubbs leaves Ginko with them while he takes Lulu to get the Amadeus. Ginko taunts them by setting some papers on fire with a lamp and then goes into the next room. MacGyver spots a CO2 extinguisher in the roof and knocks the lamp into the wastepaper basket. The flames set off the fire extinguisher and the CO2 forces the air out of the room, asphyxiating Ginko when he rushes in. MacGyver and Izzy hold their breath, cut their ropes with a table saw, and get out, pulling Ginko to safety. MacGyver knows where they're going and heads to the club where the party was.
At the club building, Tubbs forces Lulu to get the Amadeus. MacGyver pulls up outside as the violinist plays it and Tubbs immediately identifies it by the sound. He holds everyone at gunpoint and forces the violinist to give the Amadeus to Lulu. MacGyver drops in and Tubbs open fire, knocking Lulu aside. MacGyver wrecks the elevator with a wastepaper basket to prevent Tubbs from escaping. When the crook runs out of bullets, he tries to climb up the fountain. When that fails, he threatens to destroy the Amadeus. Lulu starts psychoanalyzing Tubbs, pointing out he's the son of a cafeteria worker. Tubbs panics and drops the Amadeus, and MacGyver catches it just in time.
Later, Wilt and MacGyver are biking again and Wilt is doing much better. He's eager to impress the women, and Lulu drives up in the car she's now using as a driver instructor. MacGyver introduces them and lets Wilt take over.