Jackie Kimball is a likable, normal 17-year-old girl in every way but one: she has been in love all her life with her brother Matthew, one year older than her. Matthew is bringing his new girlfriend Yolanda home to dinner at the Kimball house, and Jackie's melodramatic anguish disrupts the family's preparations. Surprisingly sociable during the dinner, Jackie later confronts her brother tearfully in the attic room that is their traditional meeting place. Matthew and Jackie have been symbiotically close all their lives, but Matthew doesn't share Jackie's incestuous inclinations, and Jackie has no choice but to deal with the intrusion of adult life upon their childhood intimacy. Long widowed, Jackie's mother Alice is a sympathetic but detached presence, often found at her writing desk, drinking coffee and composing letters and journals. An older brother, Will, is an exchange student abroad; sister Jeanne, impatient with Jackie's flamboyance, is poised to leave home soon. Though Jackie makes little effort to hide her love for Matthew, the family prefers to interpret the attraction as a long-standing childhood phase. Jackie has school friends, but no interest in other boys. Matthew's unexpected breakup with Yolanda gives Jackie a temporary reprieve from her grief, and brother and sister spend a pleasant summer together, capped by an idyllic evening out at a concert. Always monitoring Matthew for any sign that he might become receptive to her overtures, Jackie is filled with melancholy as summer wanes and Matthew's departure for college approaches. Jackie takes the separation hard, and her concerned mother sends her to psychotherapy. Though the therapy is paralyzed at first by her habitual secrecy about her feelings for Matthew, Jackie eventually becomes close to her therapist Linda and develops a fascination with the therapeutic process. Meanwhile, she and Matthew keep up contact via video letters and a host of electronic media. Out of restlessness, Jackie tries her hand with boys, and manages to seduce an attractive classmate named Tristan. Though she learns that she enjoys sex, she has little emotion invested in this new pastime, and she does not hesitate to alienate Tristan when Matthew returns on vacation. Delighted at Matthew's return, Jackie regales him with tales of her sexual explorations. Encouraged at Matthew's unfazed response, and emboldened by her recent experiences, Jackie makes a final attempt to attain her life-long goal.