In Salford, 17-year-old Jo, Rita Tushingham, struggles through an outdoor game of netball at her all-girls school. When she gets home, she hears her self-centered mother, Helen (Dora Bryan), arguing with their landlady (Margo Cunningham) about overdue rent and Helen's frequent visitors. After the landlady leaves, Jo and Helen slip out the window and ride a bus across town, a pattern that seems to define their turbulent relationship.
When Jo and Helen reach their shabby new flat, Jimmy, a young Black sailor, sees Jo struggling with her suitcases and comes to her aid. Later that evening, Helen brings her new boyfriend, Peter (Robert Stephens), home after a night in the pub, but Peter leaves after realizing that Helen is a mother. Jo and Helen go to sleep in the bed they share, a cramped arrangement that foreshadows the fragility of their household.
After being kept after class for mocking her teacher, Jo trips and scrapes her knee as she walks home. She limps past the Manchester Ship Canal, where Jimmy disembarks from the ship on which he works as a cook, and he invites her aboard. They begin a brief courtship, and Jimmy gives Jo an engagement ring that she wears on a ribbon around her neck.
Jo joins Helen and Peter on a weekend trip to Blackpool with friends. Peter gives Helen an ultimatum, saying she must choose between him and her daughter; Helen sends Jo home alone. Jimmy is waiting when Jo arrives in Salford, and they spend the night together. In the morning, Jo watches him board his ship and depart. Helen returns just long enough to pack before leaving to marry and honeymoon, with plans to live in a suburban bungalow with Peter.
Left to fend for herself, Jo leaves school, finds a job in a shoe shop, and moves into a loft apartment in a former workshop. She meets Geoffrey Ingham, a gay textile design student, and invites him to live with her after learning he has been evicted due to his sexuality. Jo discovers she is pregnant by Jimmy. Geoff offers to marry her; she declines, though she lets him take care of her in other ways. After Jo has an outburst in which she says she does not want to be either a mother or a woman, Geoff tracks down Helen. Helen comes to visit Jo, and they almost immediately have a row. An inebriated Peter enters, takes back some money Helen offered Jo, and states that Jo will not be allowed to move into his house. Before they leave, Helen offers to stay with Jo, but Jo refuses; once alone, Peter gives Helen the same ultimatum as in Blackpool, and she again chooses him.
On Guy Fawkes Night, with Jo's due date fast approaching, Helen reappears. Her marriage to Peter has fallen apart, and she is intent on moving in with Jo and pushing out Geoff, with whom she has a shouting match. Although Jo says she would prefer that Geoff stay, he packs his things and quietly leaves, stating that she will need someone with her who has gone through childbirth. Nervously, Jo tells Helen that her baby will be Black; disturbed by this revelation, Helen leaves to buy alcohol. Jo notices Geoff's belongings are gone and finds his goodbye note. She goes outside, but only sees some children with fireworks around a bonfire. From the shadows, Geoff watches Helen return from the off-licence, and then sneaks away unseen. One of the children gives Jo a sparkler, and she solemnly watches it burn out.
