When the Garretts move into the house beside Samantha Reed's, Samantha is fascinated by the family of seven's hectic lifestyle, which is so different from her scheduled and carefully planned single-parent home. Samantha's mother, Grace, tells Samantha and her sister, Tracy, that the family with the messy yard will bring down property values. Samantha is forbidden from playing with the Garrett kids, but she watches the family from her window and feels she knows them even though they never meet.
Ten years later, Samantha is 17 and plans to get a job during the summer before her senior year of high school. She doesn't need to work since her family's wealth comes from Grace's trust fund, but Grace likes her daughters to have full schedules. Grace is now a state senator campaigning for a second term, and Tracy is waitressing on Martha's Vineyard before she leaves for college. The Garretts have eight children: Joel, Alice, Jase, Andy (Andrea), Duff, Harry, George and Patsy.
While home alone one night, Samantha hears sounds outside and opens the front door to find her mother and a younger man kissing passionately. The man is Clay Tucker, her mother's new political adviser and boyfriend. Samantha becomes annoyed when Clay acts condescendingly toward her, so she climbs through her bedroom window to her private spot, the roof. Jase Garrett sees her from his house and joins her. While Samantha thinks the circumstances are bizarre, she tells Jase about Clay and is surprised by how easy it is to talk to him.
A few days later, Samantha sees Jase working on his older brother's motorcycle while he is baby-sitting his younger siblings. Jase invites her into his house, where Samantha is taken aback by how different their two households are. The Garretts' house is chaotic, loud, messy and crowded, while the Reeds' house is organized, sterile and far too big for three people.
When Mrs. Garrett comes home, she and Samantha talk as if they have always known each other for years. Mrs. Garrett asks Samantha if she is willing to baby-sit her younger children when the older ones are busy, and Samantha agrees, knowing that her mother would object if she found out.
When she's not working as a waitress or a lifeguard, Samantha baby-sits the younger Garrett kids and becomes close to Jase. Mrs. Garrett asks Samantha and Jase to follow Andy on her first date, and this assignment becomes their first date as well. Jase sneaks over to Samantha's roof, and Samantha sneaks out of her house to swim with Jase in the Garretts' pool or in a nearby lake where the two share their first kiss.
Not only does Samantha keep the relationship a secret from her mother, she keeps it from her best friend, Nan Mason. She justifies the secrecy by telling herself that Nan has enough problems of her own. Nan is worried about her own relationship with her boyfriend, Daniel, and concerned about her twin brother Tim's downward spiral into alcohol and drug abuse. She's also worried about getting into a good college so she can escape from her family and hometown.
Tim can't keep a job, has been kicked out of several private schools and even though he is frequently drunk or high, his parents do not notice. They give him money to take Samantha and Nan to the movies, but Tim decides to drive to New Hampshire to buy alcohol instead. As Tim speeds down the highway, the girls beg him to pull over. He only drives faster and more erratically until he sees police cars. Then he pulls into a truck stop and steps out of the car to relieve himself. Because neither of the girls knows how to drive, and Samantha is afraid Tim will get behind the wheel again, she throws the keys into the bushes and calls Jase for help.
By the time Jase and Alice meet them, Tim has passed out. Alice takes Tim and Nan home, while Jase hotwires Tim's car and drives Samantha home. The next day at Samantha's house, Tim apologizes for his behavior and admits that he has to get his life together. Nan is upset that Samantha never told her about Jase, and for the first time, Samantha notices that Nan is jealous of her. Later, Nan tells Samantha that she is tired of Samantha being rich, beautiful, having the perfect life, perfect body, perfect grade-point average and never having to work hard for anything. When Jase also shows up at Samantha's house, he suggests that Tim get a job at the Garretts' hardware store. Samantha also says that Tim could work for her mother's campaign, and Tim agrees to do both.
That night, when Jase sneaks into Samantha's room through her window, he asks her if she has been keeping him a secret from everyone because she is ashamed of him. Samantha denies it, and they fall asleep in her bed together. The next morning, they kiss and undress. Samantha tells Jase that she wants to have sex, and he tells her that he also wants to, but not in a rush. After they discover they are both virgins and agree to take some time before having sex, Jase leaves. A few days later, Jase and Samantha buy condoms at the local drug store.
Tim gets the job working for Grace's campaign and interviews with Mr. Garrett for a job in the hardware store. Mr. Garrett hires Tim under the condition that he attend 90 Alcoholics Anonymous meetings in 90 days, and Tim reluctantly agrees.
As Samantha returns home from a political event with Grace, Jase stops by her house on his brother's motorcycle, and she is forced to finally introduce him to her mother. Jase invites Samantha for a ride, and when she returns home, Grace is furious. She questions Samantha about her relationship with Jase and forbids her to see him again. To make it clear that she has no intention of ending the relationship, Samantha brings Jase back to her house so he can meet Grace properly.
Samantha and Jase grow even closer. When Grace leaves town for a campaign event, Samantha invites Jase to her house, and they have sex for the first time. A few days later, Tim tells Samantha that he quit working for Grace’s campaign. Although Tim was good at the job, he hated working for Clay because of Clay's manipulative campaign tactics and his plans to destroy the opponent's political career. Tim feels he has done enough bad things in his life and does not want to add to it by being a part of Clay's plans.
Samantha soon discovers that Nan habitually cheats on tests and that all her award-winning papers and essays have been stolen from Tim. When Samantha confronts her, Nan becomes angry and ends their friendship.
Samantha attends a political event a few days later where both Grace and Clay have been drinking. Since she has had less to drink than Clay, Grace volunteers to drive home, and Samantha falls asleep in the back seat. She wakes up when the car hits something and Grace screams. Clay exits the car and then instructs Grace to put the car in reverse and pull away. He tells Samantha to go back to sleep and assures her and her mother that they haven't hit anything.
A short time later, Jase calls Samantha and asks her to baby-sit the younger children. Samantha learns that Mr. Garrett has been a victim of a hit-and-run and is unconscious in the hospital. Samantha pushes away the thought that Grace could have hit Mr. Garrett with her car, but a week later, she overhears Clay and Grace talking about the accident. Grace tells Clay that what they have done does not feel right, but Clay assures her that she can do more good for more people if she is re-elected.
When Grace walks away, Clay confronts Samantha because he knows she has been listening. He tells her that the Republican Party is interested in Grace because she has looks, style and substance, and that she could easily become a national candidate. But if anyone finds out about the accident, her mother could be arrested.
After the accident, the Garrett household is in turmoil. Mrs. Garrett and the older children are frequently at the hospital, and Samantha baby-sits when she can. The younger children start acting out, and Jase is extremely stressed out about his family's situation. Additionally, there are financial concerns because the Garretts have no health insurance, Mrs. Garrett is pregnant and the hardware store has been struggling to turn a profit.
Samantha is wracked with guilt over what she knows. She tries to talk to her mom and Clay again about how wrong it is for them to hide this accident, but Clay threatens to pull some of the Garretts' hardware store contracts if Samantha does not breakup with Jase. This would place the family in even more dire financial straits, so she tells Jase that she can't see him anymore.
After the breakup, Samantha becomes depressed, quits her jobs and spends hours in her room. When Tim comes over to talk, Samantha tells him everything. Tim convinces Samantha to tell Jase the truth, which she does, and Jase forgives her. When Samantha tells Grace that Jase knows the truth, Grace calls Clay. Clay tries to convince Jase that they should all keep the secret because if Grace suffers, Samantha will suffer, too. Both Samantha and Jase refuse to keep silent, so Clay suggests spinning the situation by planning a press conference where Grace would confess what she did. He says everyone loves a repentant sinner. Jase doesn't agree to the plan, and he and Samantha leave. When Grace decides to talk to the Garretts, Clay disagrees and they break up.
After Grace confesses everything to Mrs. Garrett, the Garretts hold a family meeting and decide to keep the matter private. Grace agrees to cover all of Mr. Garrett's medical bills and the additional expenses of hiring someone to work at the hardware store. She also agrees to drop out of the race. Clay writes Grace’s resignation speech and starts working for her opponent's campaign.
When Grace announces that she is selling the house, it doesn't bother Samantha. What she loved most about the house was the view of the Garretts’ home, but she is not a watcher anymore. What she has with Jase is real, and that won't change.