Arthur Bartley, a sensitive adolescent, comes home from school one day to find that his father Malcolm has put his beloved dog to sleep. Malcolm, a former Army major, treats his son like one of his enlistees, thus alienating the boy. As Arthur and his father clash, Lillian, Arthur's sister, blissfully readies for her wedding to dentist Axel Sorenson. That night, Arthur's smart aleck friend Ernie comes to the house, and using the pretense that they have to study, the boys disappear into the cellar, where they play poker and drink beer. Ernie, feigning an aura of sophistication, boasts that he has arranged for a friend to get an abortion. Soon after, Janet Willard, an earnest young girl who has a crush on Arthur, comes to the cellar to ask Ernie to forge her father's signature on an absentee excuse from school. After Ernie leaves, Janet flatters Arthur into kissing her. Upon returning home, Janet rebels when her father, Professor Jim Willard, compares her to his angelic late wife. Janet worries that her erudite father will intimidate her friends with his aloof, intellectual demeanor. Later, at a school basketball game, Janet watches Arthur with adoring eyes as he plays with the team. Janet waits for Arthur after the game, and when he offers to walk her home, she asks if they can go steady. Janet then confides that she is a virgin and asks Arthur if he has ever had sex. At first Arthur claims that he is sexually experienced, but then confesses that he is a virgin, too. They laugh at their response, then embrace and make love. Some months later at the school dance, Janet moodily runs off to the library, and when Arthur follows, he finds her studying a book about pregnancy. When Janet insists on hiding her condition from her father, they decide to apply for a marriage license, but are turned away because they are underage. As Janet becomes more despondent, Arthur asks Ernie to arrange for an abortion. When Ernie denounces abortion as murder, Arthur, provoked, attacks him, and Ernie admits that he was bluffing about knowing an abortionist. Desperate, Arthur begs Ernie for help and together they locate a soda jerk who offers to arrange an abortion for $150. After selling their possessions, the boys are short $90. Still opposed to the idea of an abortion, Ernie admonishes Arthur to marry Janet, but Arthur protests that he is not ready to rear a child. Ernie finally convinces Arthur to tell his parents about the baby, but when he tries to raise the issue with his mother Jessie, she is so engrossed with Lillian's wedding that she misunderstands and thinks that he is asking for advice about sex. Arthur next turns to his father, who is so preoccupied with the cost of the wedding that he refuses to let Arthur speak and instead advises him to enlist in the Army, where his financial future will be assured. Desperate, Arthur steals a blank check from his father and has Ernie forge the major's signature. After the wedding, Lillian and Axel leave for their honeymoon while Janet anxiously awaits the car that will take her to the abortionist. When the vehicle arrives, Janet begs Arthur to cancel the abortion. She then resolutely climbs in and drives away, and Ernie chastises Arthur for lacking the courage to tell his parents the truth. When the banker presents Malcolm with the forged check, Malcolm confronts Arthur, who breaks into hysterics. Alarmed, Malcolm shows concern and Arthur finally tells him about the abortion. After eliciting the location of the abortionist from the soda jerk, Malcolm, Professor Willard and Arthur speed to the doctor's office, arriving just in time to prevent the operation. They take the sedated Janet home, where Professor Willard and the Bartleys engage in self-recrimination. Realizing that they failed Arthur when he turned to them for help, the Bartleys worry that fatherhood will severely curtail their son's future. After Professor Willard vows to abide by his daughter's wishes, Janet awakens and declares that she initiated the sexual relationship and therefore Arthur should not be held responsible. Soon after, Arthur learns that Janet has left town to stay with an aunt while awaiting the delivery of their baby. Stricken with a new sense of responsibility, Arthur decides to meet Janet's train at its next stop and marry her. With his father's blessings, Arthur hurries to the station, and when the train stops, Janet looks up and is overjoyed to see Arthur.