Katherine and her friends engage in many discussions about sexual topics, such as condoms, getting laid, making out and losing their virginity. Erica says she thinks it might be a good idea to get laid before college because the first time is never very good anyway. Katherine's last boyfriend threatened to find another girlfriend if she wouldn't have sex with him, so she dumped him. She hears rumors that he sleeps around a lot in college.
Katherine describes each event in her sexual relationship with Michael in vivid detail. In her initial hesitancy and fear of sex, Katherine tells Michael a few times not to touch her in certain areas. She says they should save something for tomorrow. When he learns she's a virgin, he says he likes her just the same. As the weeks pass, kissing turns into petting over, and then under, clothing. One night, as Michael watches Katherine change clothes, he comments on the firmness of her bed in regards to making love. He puts his hand in her pants and tells her how much he wants her. She says she's still not ready to have sex, but he says her body is ready. He suggests they satisfy each other without going all the way. When she says no again, he accuses her of being a tease. She promises she'll make love to him soon. Katherine imagines what sex will be like and wonders if she'll groan the way she's overheard her mother groaning during sex. She's torn between wanting to sleep with Michael and being afraid.
When Michael invites Katherine on a ski trip, Dad seems upset. Erica says Katherine's dad is hedging because dads can't stand to think of their little girls having sex. Katherine assures her dad that Michael isn't a sex fiend, so he should stop worrying. Katherine gets her period on the ski trip and tells Michael, hoping he's not too disappointed. He comes into her room later that night for some intimate touching, and he tells her he loves her. She doesn't consent to having sex that night, but they sleep in each other's arms. The next night, they lie in bed together in just underpants and experience orgasms through heavy petting. Then Michael shows her how to use her hand to help him achieve an orgasm. She graphically describes everything about the experience. They promise to love each other forever. When Katherine returns from the ski trip, Erica says she can tell her friend is still a virgin.
Michael reveals that he had VD twice but got it from the same girl. They continue in the manner they have a few more times and in different locations before they finally have intercourse. She doesn't have an orgasm. She tells him she's not disappointed, but truthfully, she'd hoped her first time would be perfect. She goes to the bathroom and wipes away the blood. Even though she feels let down, she's glad the first time is over. She says Michael is probably right, and this would just take practice. She says she can't imagine what a first time would be like with someone she didn't love.
Katherine asks her mom if she was a virgin when she got married. Mom says she was a virgin until she got engaged, but that Dad had more experience since that's what men were expected to do. Mom makes several references to her day, when there were double standards for men and women. The good girls who didn't sleep around were the marrying kind, but men were supposed to get some pre-marriage sexual experience. Katherine asks Mom if she would do it again if she could do it over. Mom says she doesn't know. She tells Katherine that sex is a commitment; you can never just go back to holding hands. She says you give yourself physically and mentally, and it makes you vulnerable. Mom says she won't tell Katherine what is the right or wrong thing to do. She just urges her to act responsibly either way. Later, Mom gives her a newspaper article about sexual liberation and the right to say no. The author of the article asks adolescents four questions when counseling them: "Is sex necessary for the relationship?" "What should a person expect from sex?" "Where will you get help if you need it?" "Have you thought about how this relationship will end?" Katherine doesn't like the last question's assumption that the relationship must end. The author of the article also writes that enjoyable, orgasmic lovemaking requires practice and mutual education. Mom later discusses the article with her.
Erica is interested in having sex with Michael's friend, Artie. When Artie doesn't make any moves, she asks him if he's queer. He says no; he's just scared. She tells him she'll help him figure it out, and she begins playing strip poker and engaging in sexual touching with him. She later tells Katherine that she thinks he's impotent, but she can help him out. Erica gets a call from Katherine's ex, who is back from college and looking for sexual action. Erica doesn't sleep with him but says he has a perpetual hard-on.
Erica finds out that her promiscuous cousin, Sybil, is pregnant and is unable to identify the father. Erica says Sybil is too far along to have an abortion. Sybil didn't tell anyone sooner because she wanted to have the baby and knew her parents would have insisted on an abortion if they found out. Erica says Sybil knows she can't keep the baby. She'll put it up for adoption, but she wants to have the experience of delivering a baby. Katherine says she'd have an abortion, and Erica agrees she would, too. Erica says her mother is so concerned after learning about Sybil that she's taking Erica to the gynecologist and getting her on the pill. Erica tells her mom she‘s a virgin, but her mom says she'd feel better if Erica was prepared for college in every way. Erica is fine with that, liking the idea of being ready for anything. She hopes it will make Artie feel more secure, too. Katherine and Erica visit Sybil in the hospital after she's had her baby. She tells them the movies are wrong about it hurting to give birth. She just pushed and it popped right out. She tells them she's getting an IUD so she won't get pregnant again, because she has no intention of giving up sex. She says next time she gets pregnant, she intends to be able to keep the baby. She tearfully says she couldn't do that now, because it wouldn't be fair. In a letter to Katherine that summer, Erica indicates Sybil doesn't want to talk about the baby. She thinks the whole experience was more than Sybil bargained for.
Grandma, a staunch supporter of Planned Parenthood, warns Katherine about pregnancy and venereal disease in Katherine's early relationship with Michael. Katherine, embarrassed, says they're not having sex. Grandma replies, “Yet.” Katherine is initially put off by her family's contention that her whole generation is screwing around, but her own behavior later adds credibility to their beliefs. Later, Grandma sends Katherine a package filled with Planned Parenthood pamphlets on birth control, abortion and sexually transmitted infections. She asks Katherine not to tell her parents she sent them.
Katherine mentions a girl in one of her classes who didn't know until this year that intercourse caused pregnancy, even though she'd already had sex.
Katherine calls Planned Parenthood and makes an appointment to get birth control at the Margaret Sanger Clinic. She's asked a battery of questions about her health and sexual behavior to determine what kind of birth control is best for her circumstances. She's given a gonorrhea test and a pelvic exam with a pap smear. Katherine describes the cold, uncomfortable feeling of having the vaginal speculum inserted. The doctor ends by holding a mirror between her legs to show Katherine her cervix before giving her a prescription for the pill.
As Michael and Katherine prepare for another sexual encounter, he asks her to use lotion on him. She graphically describes the experience. They try again later, and it is graphic. Katherine is thrilled by the experience and tells Michael that she never felt so close to him. Afterward, they take a shower together.
After Michael and Katherine discuss having to be apart for the summer, he's frustrated and angry and can't perform sexually. The next time they try, he has no problems. After Michael's graduation party, they go to Katherine's house. Her parents are asleep, so they lock themselves in the den and make love. After a beach party, Katherine and Michael have sex in a sleeping bag.
From tennis camp, Katherine writes to Erica that she's been thinking Erica should keep her vow about getting laid before college. She says it might be just what Erica needs right now. Erica writes back that she's been doing a lot of thinking. She doesn't want to have sex just for the h--- of it but to have something special like Katherine and Michael.
Later, Katherine starts having sexual dreams about Theo, even though she's trying to keep her mind on Michael. She says that in her dream, she does things to him she'd only read about. Theo offers emotional comfort to her after her grandpa dies, and she kisses him. He stops her, saying he doesn't want a physical relationship with her because she feels comforted. He later tells her that it's common for people dealing with death to want to prove they're alive by having sex. When Michael pays a surprise visit to Katherine, they start getting physical, graphically, but then she stops him. She tells him that she's interested in Theo. Michael thinks she means her grandfather. He tells her that grandpa would want them to be together. Katherine breaks up with him, and he tells her he's slept with many others. She doesn't know if it's true or if he's just trying to hurt her.