A bunch of senior high school students are at the empty beach house. The Wilsons are out of town and the kids, Brett, Adam, Jonathan, and Holly, are drinking. They realize that one of them, ninth-grader Lisa Woodman, has passed out drunk. Holly, who brought Lisa, admits that she couldn't get rid of her but the ringleader, Brett Reynolds, says it's not a problem. They hear a car pull up outside and see the maid coming in. Brett tells them to split and meet him at the club while he grabs the loot. Holly goes to get Lisa but Lisa falls behind and collapse unconscious. Upstairs, Brett grabs the stolen jewelry and money and puts it in a garbage bag. The maid sees him and he kicks her down the stairs. He steps over her body and leaves.
Later at the police station, Captain Kelly calls MacGyver in and tells him the girl he arrested involved in a string of burglaries insists on only talking to him. They bring in Lisa, who insists nothing is going on but wanted MacGyver to come in because she figured he'd listen. Lisa explains she's on the outs with her parents and knew the Wilsons were on vacation, but her friend Darlene invited her to stay. She claims she was tired and left the door unlocked, but Kelly says they smelled liquor on her breath. Lisa claims she was eating candy cordials and asks MacGyver if she's ever lied to him.
Brett and his gang meet back at the Safari Gun & Travel Club. They note that Brett flunked out of Stanford and his father cut him off, but Brett says that he never went to class. They stash the newest loot with the rest of their stolen money and Brett has Holly call and check on Lisa. She tells Brett and the others that Lisa isn't at home. Brett tells Holly to talk to Lisa, and if she can't make things right, they'll eliminate her.
MacGyver takes Lisa home and her rich parents Eric and Katherine demand answers. MacGyver explains what happened and Lisa figures they think she's guilty. They know that she wasn't in school that today. MacGyver warns that there'll be a hearing and Lisa smartmouths her parents. They send her to her room and tell MacGyver that Lisa's been falling behind in her grades and been absent constantly. Out in the kitchen, Lisa pours herself a drink.
MacGyver goes to the Wilson house where Kelly tells him that the Wilsons have never heard of Lisa and don't have a daughter named Darlene. The officer's arresting report confirms that Lisa was drunk. Kelly knows all about it and admits high school drinking is a major problem. The maid is in intensive care and Lisa is the prime suspect in the robbery and the assault on the maid.
MacGyver tries to find Lisa as she gets out of school. Holly approaches Lisa, who wants to know what happened and why they left her at the Wilson house. Holly claims that she had no idea Lisa was arrested and that she and the others had nothing to do with the robbery. Before Holly can find out what else Lisa told the police, MacGyver finds Lisa and offers her a ride home so they could talk. He wonders why she lied to him and wants to know what really happened. Lisa lies again, saying she was drinking, got sick and crawled into the house. MacGyver talks about how he tried alcohol once with a friend and hated it. His friend was in an accident five years later and crippled his girlfriend.
MacGyver takes her to the Challenger Center and has her take a test about her drug use habits. Lisa lies on the tests and MacGyver takes her home. Katherine is waiting for her and talks to her in private. MacGyver goes to talk to Eric and tells him that Lisa has a drinking problem. Eric insists it's impossible and he would have known. MacGyver points out that parents often don't know. They're interrupted when Lisa and Katherine come in. Katherine reveals that Lisa has been forging her signature on credit card charges for food for her friends. Eric tells them that MacGyver thinks Lisa is an alcoholic, angering Lisa. When he notes that some researchers think alcoholism is genetic, Katherine and Eric think he's blaming them and order him out.
At the Safari Club, Brett is checking the travel records of the club members looking for new houses to rob. Holly comes in and notes that he injured the maid. She tells Brett that MacGyver interrupted them before she could find out what Lisa told the cops. Brett goes to check on Lisa.
Lisa slips out of her house as Brett and Holly pull up. Brett suggests they skip school and go to the beach and convince Lisa to go with them.
MacGyver tells Kelly that Lisa is hanging out with the thieves and needs his help to find out who they are. Kelly has the travel vouchers of the victims and MacGyver gets permission to go over them.
At the beach, Brett plans to get Lisa drunk so she'll tell him what he wants to know. He tries to feed her drinks but she say she can't drink, insisting she isn't going to give MacGyver and her parents the satisfaction of thinking she's a drunk. Lisa insists she can stop any time she wants but Brett taunts her into drinking. She insists she'll just drink one beer and then leave.
MacGyver goes over the vouchers and determines that all of the vacationing victims made travel arrangements through the Safari Club. Kelly gets a call that the Wilson maid died and Homicide wants to talk to Lisa. He asks MacGyver to bring Lisa in while he checks out the travel agency.
On the beach, Lisa is drunk and trying to dance. Brett gets her to say that MacGyver isn't a cop. Jonathan arrives with a report on the house they were going to rob. He's also heard that the maid died. Brett tells him that he'll take care of everything. Holly approaches Brett and he tells her to go home and he'll call her later. She gets him to admit that the maid died and they're going to have to do something about Lisa. He warns her that if Lisa talks, Holly will go to the jail with the rest of them and he'll take care of the situation.
MacGyver goes to see Holly and discovers her packing to leave. She claims she has no idea where Lisa is but MacGyver knows she's lying. Holly insists that Lisa is a bratty ninth-grader who definitely isn't her friend. She drops her belongings and MacGyver spots a photo of her with Brett at the Safari Club. He gets Holly to admit that Brett has the run of the club, which belongs to his father. Holly tries to leave and MacGyver wants to know what's going on. She finally breaks down and admits that Brett is going to do something to Lisa.
Brett breaks into the new victims' beach house and finds their car keys. Jonathan and Adam bring a drunken Lisa into the house and Brett claims that the house belongs to his uncle. Brett tells his accomplices that they're going to make it look like Lisa died in an accident and then implicate her in the robberies. Lisa lies down and passes out.
Kelly is at the Safari Club and MacGyver calls to tell him Lisa's life is in danger. He talks to the travel agent, Betty, and has her check to see whose files Brett has recently accessed. She comes up with an address and MacGyver heads to the house.
Brett and the others haul Lisa down to the garage, put her in the owners' SuV, and turn the engine on. The garage fills with carbon monoxide and Brett tells Jonathan and Adam to meet him back at the Safari Club while he gets his bag. MacGyver arrives and discovers the jimmied door. He comes inside while Brett collects his bag. Brett spots MacGyver and shoots at him. MacGyver ducks and then hides in a fireplace. As Brett searches for him, MacGyver lures him in and then rigs a figurine so that a light makes it appear that MacGyver's shadow is on a screen. Brett comes in and opens fire and MacGyver leaps on him and knocks him out.
In the garage, Lisa wakes up and tries to get out of the SUV. She starts it up and throws it into gear and the SUV crashes through the garage and over an embankment. The water is a hundred feet below and the SUV hangs by a thread. MacGyver tells Lisa not to move and then unfastens the guard chain from the posts. He fastens it around the SUV's hitch just as the vehicle breaks loose. The chain stops it halfway down the embankment. MacGyver climbs down on a section of chain fence. He tells the injured and partially stunned Lisa to open the door. She can't and he has her open the window. Once it's open, MacGyver pulls her out just as the chain gives way and the SUV plummets into the waters below.
Later, the police take away Brett. Lisa admits to MacGyver that she has a drinking problem and he says it's a good start.