Chapters 1-4

At the beginning of Forever …, the protagonist, Katherine, and her best friend Erica, (both seniors in high school) attend a New Year's Eve party. The party is given by Erica's cousin Sybil, who is described as having a poor self-image because she is overweight and tends to be sexually promiscuous in order to feel loved. At the party, Katherine meets Michael, a friend of Sybil. The next day, Michael asks Katherine to go for a drive with him. Afterward, he kisses Katherine before saying good-bye and tells Katherine that she is delicious.

Katherine is at home, telling her mother that she has met a nice boy and that she has a date with him that weekend. Katherine describes her mother, whose name is Diana and who works in the children's room at the local library, as thin and tall and not necessarily athletic. Jamie, Katherine's younger sister, is also introduced. Jamie is in the seventh grade and is artistic, unlike Katherine. Jamie and Katherine, despite their age difference, appear to be friends. They respect one another's talents and are supportive of one another. Jamie volunteers, for example, to embroider a design on Katherine's jeans to wear on her first official date with Michael.

Katherine then talks about Tommy Aronson, the boy whom she dated before she met Michael. Her relationship with Tommy was not good. Tommy dated Katherine, she finally discovered, only to have sex with her. When Katherine made it clear that she did not want to have sex with him, Tommy dropped her for another girl, presumably one who would. Unlike Tommy, Michael makes Katherine feel good about herself. He is attentive and caring.

Katherine invites Michael to come back to her house after their date. She takes him to a private room downstairs that has a lock on the door. They start to kiss, but Katherine stops Michael when he goes a little too fast for her. He asks if she is a virgin, to which Katherine answers yes.

Katherine introduces her father, who is a pharmacist. Later, Katherine invites Michael and Erica over to the house. Michael brings Artie with him. Erica and Artie play backgammon in the kitchen, while Michael and Katherine retreat to the downstairs room. They kiss, but Katherine stops Michael again because he is moving too fast for her. Michael and Artie leave, and Erica spends the night. Erica says that Artie seems shy because he did not even try to kiss her. Then Katherine and Erica discuss their feelings about sex. Erica says that girls do not have to be in love to have sex, but Katherine disagrees.

Chapters 5-7

Jamie plans a big dinner with her grandmother, who has come to stay with the girls while their parents are away. Michael picks Katherine up one night at the hospital where she works as a candy striper. Michael invites Katherine to his school's play. Artie has the lead role, so Katherine then invites Erica to come along. When they get home, Katherine introduces Michael to her grandmother, who later warns Katherine to be careful about pregnancy and venereal diseases. Katherine is a little embarrassed and disturbed that her grandmother assumes that Katherine will have sex.

After Michael leaves, Jamie tells Katherine that she wishes Michael had a younger brother. When Jamie asks if Katherine and Michael are having sex, Katherine becomes upset. Jamie tells her that Katherine's generation is too hung up on sex.

By chapter six, Erica is frustrated in her relationship with Artie. He still has not kissed her, so she tells Katherine that she plans on doing something about it. The two girls then go to see Artie in the school play. Sybil and Elizabeth are also in it. When Katherine sees Elizabeth, her jealousy begins to swell. By the time the play is over and everyone has gone to Elizabeth's house for a party, Katherine has trouble controlling her emotions. Everyone congratulates Artie for his wonderful performance, but this is not a sufficient distraction for Katherine, who can barely talk because she is so emotional.

Michael and Katherine leave the party early and end up at Katherine's house. They make out for awhile, but once again Katherine stops Michael when she thinks he is going too far. She tells him that she might be physically ready to have sex, but she also wants to be mentally ready, too. Later, when she is alone, she realizes that the thought of sex frightens her.

In the next chapter, Michael invites Katherine to go skiing with him and his sister and her husband in Vermont. Katherine would be away from home for three nights, so her parents want to think it over before giving Katherine an answer. As Katherine waits for her parents' answer, she talks to Erica about the tension she is feeling. Erica informs Katherine that Artie has told her that he might be gay. He is in the process of trying to find out what his sexual feelings are. Erica has told Artie that she will help him find out. Later, Katherine finds out that her parents have agreed to let her go.

Chapters 8-9

The next two chapters are set in Vermont. Katherine and Michael have adjoining bedrooms and before Katherine falls asleep, Michael comes in and asks if he can be with her. Katherine tells him not to get too physically aroused because she does not want to have sex. That is when Michael tells Katherine that he loves her. Katherine is not ready to say this back to Michael, although she feels she loves him. They fall asleep in one another's arms.

Before they go skiing the next day, Sharon and Katherine have a talk. Sharon tells Katherine that Michael is a good boy and is also very vulnerable; and she does not want to see Michael get hurt. This comment concerns Katherine, who wonders if Sharon thinks that Katherine is just using Michael.

Michael teaches Katherine to ski. They are on the slopes all day. At night, they return to the apartment to find Ike and Sharon smoking marijuana. Both Katherine and Michael have tried it before, but they pass on the invitation to join the other two. Instead, they go to bed. Michael climbs into bed with Katherine, and they make out. This time, they both reach climaxes without having full intercourse. Before going to sleep, Katherine tells Michael that she loves him.

Chapters 10-13

When Katherine returns from Vermont, her father confesses that he is concerned that Katherine is getting too involved with Michael. He does not want to see her tied down to one boy, he tells her. The next morning, Katherine's mother explains that Katherine's father just wants to see her spending time with more people. On the way to school, Katherine asks if her mom was a virgin when she married Katherine's father. Her mother says she was until they were engaged. Katherine's father was not a virgin, however. But Katherine's mother explains that there were different standards for girls and boys back then. It was all right for boys to have sex. But girls were supposed to be virgins when they got married. Katherine's mom then warns Katherine that having sex with someone can make her more vulnerable. She also tells Katherine that she is not going to tell Katherine what to do. It is up to her, but Katherine should make sure that she is ready for it.

Later, Erica says she cannot believe that Katherine is still a virgin, although Katherine has not admitted whether she is. Erica says that she can tell, however, that Katherine has not yet had sex. Katherine then tells Erica that what she does with Michael is private, and she does not want to share it. She also confesses to Erica that she really loves Michael. Erica tells Katherine that she believes that Artie is not gay but rather impotent.

On a double date, Erica announces that Artie has been accepted at the American Academy of Dramatic Arts, a school that Artie would love to attend. Artie's father, however, refuses to let him go. When Erica tells Artie that he should stand up to his father, Michael tells Erica to leave it alone. Later, Katherine tells Michael that she has never seen Artie so depressed.

Michael goes away for ten days with his sister. It is a ski trip, one that will help Michael get his instructor's certificate. Katherine stays busy, but she misses him a lot. Katherine's father again makes the statement that he wishes Katherine would see someone in addition to Michael. Katherine's mother makes the point that Katherine will have to learn to live without Michael when she goes away to college in the fall. This comment makes Katherine go to her counselor to try to apply to the University of Vermont. She wants to go to school wherever Michael goes. When Katherine is told that she will need her parents' permission to apply, Katherine assumes they will support her change of mind. But they do not.

Michael comes back from the ski trip early and surprises Katherine. They go on a date, and Katherine cracks a joke about venereal disease (VD), but Michael does not find it funny. Then he confesses that he once had what he refers to as the clap.

Katherine and Michael end up at Michael's sister's apartment. Sharon and Ike are out of town. Katherine and Michael spend time in bed together, but it is not until the next night that Katherine finally loses her virginity. The experience is a little disappointing, and Katherine wonders why everyone makes such a big deal about it.

Katherine's old boyfriend, Tommy Aronson, calls at the beginning of chapter 13. He is back in town and wants to see Katherine. She sees right through him, knowing that all he wants is sex. She turns him down for that reason and the fact that she has no interest in him any more.

Chapters 14-16

Katherine receives a package from her grandmother. It is filled with Planned Parenthood pamphlets. Katherine calls her grandmother and sets a date with her. Katherine then telephones Planned Parenthood and makes an appointment with them. In chapter fifteen, one of the clinicians at Planned Parenthood asks Katherine some personal questions about her relationship with Michael. They then discuss various birth control devices. Katherine is also tested for gonorrhea, a sexually transmitted disease. By the end of the chapter, Katherine has chosen a birth control pill to use.

Both Michael and Katherine come down with the flu. They must stay apart from one another for several days. When Michael takes Katherine out on her birthday, he gives her a present. It is a necklace that holds a small silver disk with "Katherine" engraved on one side and "Forever … Michael" on the other. Katherine tells Michael that she has a surprise for him, too. She tells him that she is now on the pill.

Katherine and Michael go to Michael's house. His parents will be gone until midnight. They make love in Michael's bed and afterward take their first shower together.

Chapters 17-19

Katherine mentions that her sister, Jamie, is going back to a summer camp in New Hampshire, but Katherine does not yet know what she will be doing for the summer. She has been job hunting without success. Michael is looking for a summer job also.

Erica, in the meantime, has found a position on the local newspaper. Erica tells Katherine that her cousin Sybil is pregnant. Sybil has been able to hide her pregnancy from everyone because she wore large-sized dresses, as she always had. Sybil is planning on giving the baby up for adoption.

Because Katherine's parents will not give her permission to apply to another college just to be with Michael, Katherine and Michael develop a plan of their own. Michael will take off one semester and work as a ski instructor in Colorado.

Katherine's father announces that he has talked to Sam Fox, the director of the summer camp that Jamie will attend. Sam tells Katherine's father that he needs a tennis counselor, since one of the counselors he had hired is sick. Katherine's father tells Sam that he is sure Katherine would love to work there. Katherine balks at the idea. It would mean being away from Michael. Katherine's father insists that Katherine take the job. She has no choice. Katherine is very upset.

Erica invites Katherine, Michael, and Artie to her house, while her parents are away. They celebrate Michael's birthday, but this depresses Artie, who sees no future for himself. Later, the couples go their separate ways to different rooms. Katherine tells Michael that she has to go to New Hampshire for the summer. Michael announces then that he accepted a summer job in North Carolina. Michael's parents wanted him to take it. Katherine and Michael resolve not to let the separation change their relationship as their parents are hoping it will.

After the boys leave, Katherine finds Erica crying in her bedroom. She has told Artie that she cannot take it anymore. She cannot help him any further. Artie then locked himself in her bathroom and threatened to kill himself. Artie later calms down, as if he were acting out a role, and tells Erica that he does not blame her.

At the beginning of chapter 19, Artie has tried to hang himself from the shower curtain rod in his bathroom. The attempt failed because the rod broke. He has been taken to a private psychiatric hospital. Both Michael and Erica feel guilty about not having done more for Artie. The chapter ends with Michael and Erica going out with Katherine to a bar and getting very drunk.

Chapters 20-26

Sybil has her baby. Erica and Katherine visit Sybil in the hospital. Sybil will miss her graduation but has decided to lose weight and to accept Smith's offer for college. She is also going to be fitted for an intrauterine device (IUD), a birth control device. She poses a strong front in giving away her baby, but both Erica and Katherine are near tears.

Katherine attends Michael's graduation. It is sad for her when both Sybil's and Artie's names are called and no one appears on stage. Katherine's graduation is held next. Shortly afterward, Erica invites Katherine and Michael to her parents' summer home on Long Beach Island. Four days after that, Katherine and her sister, Jamie, are at the New Hampshire camp.

Chapter twenty-two consists of a series of letters. Katherine and Michael exchange news and details of their lives and write about how much they are missing each other. In a letter to her parents, Katherine first mentions Theo, the head of the tennis program at the camp. She also mentions Theo to Erica. Katherine writes a quick note to Artie who is still hospitalized.

In chapter twenty-three, Katherine narrates a typical day at camp. Readers can tell that she is becoming somewhat attracted to Theo. She describes in detail what he looks like. The two of them play tennis together and go swimming. One night, Theo asks Katherine about the necklace she wears, the one that Michael gave her for her birthday. When he sees the word "Forever" engraved on one side, Theo tells her that he thinks forever is a very long time for someone as young as Katherine. Later, Katherine dreams she is making love to Theo and feels ashamed. One night, Theo asks her to slow dance with him. After the dance, Katherine runs away and cries because she does not understand her mixed emotions. When Katherine's parents come to visit, she shows them a box stuffed with letters from Michael. She confronts them by saying she bets they thought the separation would stop them from communicating. The box of letters is proof that the separation has not affected their relationship, Katherine half-heartedly believes.

Chapter twenty-four brings the news that Katherine's grandfather has died. Katherine's parents believe that it is best that neither Katherine nor Jamie come home. Grandpa did not want a funeral, and their grandmother will appreciate the solitude for a couple weeks.

Theo comforts Katherine when she tells him why she is crying. When Theo walks Katherine back to her cabin, he kisses her on the forehead. Katherine then pulls him into her and kisses him on the mouth. However, Theo gently untangles himself from her arms and tells her that he does not want her like this, implying in her time of weakness. Katherine stops writing to Michael, as she needs time to think. Finally, she writes him a letter, trying to be as honest as she can. She tells Michael that she has met someone else, but she is not sure what her emotions are. She cannot finish the letter and decides that she could never send it.

Michael surprises Katherine with a visit at the camp. He catches Katherine holding hands with Theo. Later, when Katherine and Michael are in Michael's motel room, Michael wants to make love, but Katherine cannot do it. Michael guesses that there is some other guy in her life. Michael refers to the necklace and the word "Forever." He wants to know what that means now. Michael decides that their relationship can never be the same again, although Katherine holds onto the hope that it can. Michael tells Katherine that he is not about to share her with anyone. He says she cannot have it both ways. Katherine asks if that means it is all over between them. Michael says that he thinks it is. Katherine takes off the necklace and gives it to Michael. But Michael drops it into Katherine's purse.

Katherine returns home. She accidentally bumps into Michael while she is out with Erica. Michael tells them that Artie is home. He also tells Katherine that he was offered the ski instructor position at Vail, which means he could be in Colorado during the winter. But he is not certain he will take it. He says that it all depends on, and then he does not finish his sentence. Katherine tries to explain to Michael that she will always love him. And they part.

The book ends with Katherine at home. She has just been told that Theo has called.