MacGyver drops off the Coltons' dog Frog with Ma Colton, who is returning home after a one-week family reunion. Frank, Jesse, and Billy are away, and she's on her own. As they go into her house, a young boy, Ricky, runs out with a box of baseball cards. He slips beneath a fence and hands the cards off to a teenager, T.J., who rides away on his bike. With Frog's help, MacGyver and Ma Colton capture Ricky, who explains that T.J. forced him to steal the baseball cards. Ricky got counterfeit trading cards from someone who got them from T.J., and Ricky tried to trade them back to T.J., who caught on. Ricky tells them that they can find T.J. at the Batter's Box Card Shop.
Elsewhere, Willard, and his assistant are beating up legendary baseball player Novus Reilly. They tell him that he needs to pay up on his debt to their boss, Bill Marsh. They tell him to get Reggie Jackson's baseball memorabilia collection and stop his daughter from bothering Marsh's card dealers.
Ma Colton convinces MacGyver to recover her son's stolen baseball cards since the police won't bother to take the time. MacGyver goes on ahead while she deals with Ricky. At the Batter's Box, MacGyver talks to the manager, Tim, who isn't interested in helping him find out where T.J. is. A girl, Wendy, interrupts and tells MacGyver that T.J. just made a trade with Expert Eli, a counterfeiter.
Ma Colton asks MacGyver to get Frank's baseball cards back, insisting the police will take their time investigating. She says she'll be down at the card shop shortly after she talks with Ricky's mother. At the baseball shop, T.J.'s buyer Eli collects the cards and leaves just as MacGyver arrives. MacGyver talks to the clerk, Tim, who is less than helpful. Wendy is in the room and tells MacGyver that T.J. made a trade with Eli and they both just left. When she accuses Tim of handling counterfeit memorabilia, he throws both of them out. Ma Colton arrives and Wendy convinces her to convince MacGyver to let her tag along. She takes a look at the list of stolen cards and tells Ma that they're worth $50,000.
Wendy and MacGyver go to Wendy's shop, unaware that Tim has called Marsh at his printing company. Eli arrives at the plant with the Colton baseball cards and assures Marsh that he can use them to make undetectable duplicates.
Wendy explains to MacGyver how criminals are moving into the memorabilia business and manufacturing counterfeits that they sell to unsuspecting kids. Novus comes in and MacGyver realizes that he's Wendy's father. When Novus warns that his daughter has brought in a lot of kooks that don't know baseball, MacGyver explains how he used to watch him when he played for the Mets and spotted Novus giveaway. Convinced, Novus still tells his daughter not to get involved. After he leaves, Wendy explains that her father started gambling after he retired and Marsh collected his markers. Marsh has been using them to blackmail Novus into stealing baseball memorabilia that he can counterfeit and sell. Wendy shows him one example of counterfeit memorabilia, a near-perfect Walter Johnson baseball. Wendy suggests that they put a tracking device in it, advertise it on the computer bulletin boards in return for the Colton baseball cards, and then follow the tracker to where Marsh makes his counterfeits.
Marsh and Willard try to figure out how they can force Novus to play along, and Willard warns that Wendy is closing in on their operation.
Ma Colton has Ricky promise to read a book for every card that he stole. MacGyver and Wendy arrive at her house and explain their plan. They have Ma Colton use her computer to place the advertisement for the cards.
Once Marsh agrees to the trade, MacGyver goes undercover as his nerd alias Dexter Fillmore. He meets with Eli and Willard and trades the baseball for the Colton cards. Eli gives him counterfeit cards that he's already manufactured. Once the trade is done, MacGyver goes outside and he and Wendy follow Willard when he leaves with the baseball.
At home, Novus watches the pre-recorded press conference he made with Reggie Jackson announcing Jackson is donating to the American Museum of Baseball the coming Saturday. Marsh calls Novus and tells him that he has to give him the Jackson Collection in two days or he'll be dead.
MacGyver and Wendy follow Willard to Marsh's estate. MacGyver calls Ma Colton to have her determine who lives at the address and has Wendy wait in the car for the answer while he sneaks inside. A guard dog chases MacGyver, who manages to trap it in a tool shed. He slips up to the window of Marsh's study and listens in via an air vent as Marsh and Willard discuss their plans to steal the Jackson Collection. Ma Colton calls Wendy back to tell her that Marsh owns the house. She goes in and accidentally releases the dog. She's forced to hold it off with a rake and Marsh and Willard spot her and take her prisoner. Marsh decides to use Wendy as a hostage to force Novus to steal the collection and bring it to them. They leave with the girl and MacGyver realizes that they've left the baseball in the house: he has no way to track them.
MacGyver calls to tell Novus what's going on. Novus insists that they don't call in the police and meets with MacGyver at Ma Colton's house. Before he can leave, Novus gets a call from Marsh, who gives him two hours to get the collection.
At the house, Ma Colton warns that Novus won't act rationally with his daughter in danger. When Novus doesn't show up, Ma Colton makes a call to someone she knows to find the collection.
Novus goes to the stadium where he's stored the collection. MacGyver and Reggie Jackson arrive and Novus explains Marsh's thread. Reggie convinces him to go to the authorities and leaves. However, when MacGyver goes to call the police, Novus takes off with the collection.
With time running out, MacGyver dresses up as Dexter again and goes to the Batter's Box. He offers to buy a lot of cards and throw in a thousand dollars if Tim can place the order in the next sixty seconds. When Tim gets behind, he asks to make a call and MacGyver agrees. He secretly tapes Tim dialing the phone number to contact Willard at the plant to get the counterfeit cards ordered. When Tim can't come up with the cards right away, MacGyver leaves, plays back the tape, identifies the keypad numbers from the tones, and has Ma Colton trace the number.
Novus goes to the printing plant and tries to negotiate, giving Marsh only one bat and a ball and promising the rest when Wendy is safe. Marsh threatens to cut off Wendy's hand in a cutting press and Novus quickly caves.
MacGyver gets the address from Ma Colton and sneaks into the plant. He gets close enough to secretly send Novus his own giveaway sign. Novus offers to take Willard's assistant out to his car to get the rest of the collection. MacGyver ambushes the man and knocks him out. He then turns on the press to get Willard's attention. Novus disarms Marsh while MacGyver manages to knock Willard out. Marsh runs for his car and drives away beneath the scoreboard sign for his printing company. MacGyver pitches a ball to Novus, who hits it into the sign and brings it down on Marsh's car.
Later, Novus and Wendy visit MacGyver and Ma Colton at her house. Novus assures Ma Colton that the boys' baseball cards will be kept safe at the Baseball Museum. Ricky comes back and sees Novus, and asks for an autograph. Novus is glad to sign an autograph for the boy, for free.