In the early 1950s, sixteen-year-old Lynda Mansell lives in a small English seaside town with her widowed father Hubert and younger sister, Margaret. Feisty, outspoken, and bawdy, Lynda likes to shock other people with her histrionic behaviour (bicycling on the promenade with her skirt hiked up, inviting young men to compare her legs to Betty Grable's) and vulgar speech (her favourite insults are "Up yer bum" and "Cock Off") which alienate her from her peers and her sister. Her father finds her employment at a variety of places, including a ladies' hair salon, a bus depot, and a fish and chip van, but her behaviour always loses her the job. Hubert, with whom Lynda has an adversarial relationship, unsuccessfully tries to correct Lynda's behaviour by taking her to a psychiatrist. Flashbacks reveal Lynda was close with her late mother.

Lynda returns the affections of a couple of male suitors: Brian, a boy she encounters on the promenade, and Dave, a young bus conductor to whom she loses her virginity, but the relationships fail due to the boys' immaturity, and her father warning off Dave, unbeknownst to Lynda. Meanwhile, Eric, a bookie and one of Hubert's middle-aged friends, takes an interest in Lynda. She initially refuses Eric's predatory advances, but as her relationship with her father grows increasingly strained, Lynda begins sleeping with Eric. When Hubert finds out, he tells Lynda how ashamed he is of her, and how her mother would be too if she were alive.

Lynda leaves her home to live with Eric, but instead of the affection and genuine love she craves, she is greeted with his callous behaviour. He ignores her tearful plea for comfort, seemingly only interested in having sex. Lynda eventually leaves him and gets a job as a waitress at a tea room. Eric appears and bothers Lynda, claiming he has missed her, but he stops pestering her when she reveals she is pregnant. Lynda considers an illegal abortion, but realises she cannot afford one.

Having learnt of his estranged daughter's pregnancy, Hubert arrives at the tea room demanding to speak to Lynda. Lynda denounces her father after he calls her a slut. Their argument escalates into a public spectacle, with Lynda climbing onto a table and shouting about British respectability and hypocrisy, while insulting customers. Lynda is fired, but a few customers applaud her rant, including the elderly woman who plays the tea room piano.

Desperate and down-on-her-luck, Lynda meets with her Aunt Millie, who tries to persuade Lynda to get an abortion or give the baby up for adoption, as women who have children out of wedlock are looked down upon in society, and no man will want her. Aunt Millie tells Lynda the choice is hers, but leaves her money for a termination. Lynda returns to an abortion place that she previously visited, but hesitates at the doorstep and imagines an old man and a little girl watching her.

Several months later, Lynda returns home, alighting at the bus garage where she previously worked—with a newborn baby. She passes by her former haunts, including the promenade where she used to flash her legs at the boys. Onlookers on a bowling green, Eric among them, are shocked to see Lynda defiantly pushing her baby in a pram. The film ends with Lynda ringing the do…

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