Thirty years old and single, Pauline "Poppy" Cross shares a London flat with her best friend Zoe, a fellow teacher. The film opens with a very high-spirited Poppy entering a second-hand bookshop. She attempts to engage the shop employee in a conversation and he blatantly ignores her. Despite the fact that he refuses to respond to Poppy's exceptionally sunny disposition, this does not appear to bother Poppy. She maintains her good mood even when she discovers that her bicycle has been stolen. Her main concern is not getting a new one, but the fact that she did not even get a chance to say goodbye.
Poppy decides to take driving lessons for the first time in her life. Her positive attitude is a stark contrast to that of her driving instructor, Scott. His personality is defined by his gloomy, intolerant, crude and cynical attitude. Scott is an emotionally repressed character with anger problems. He has a belief in conspiracy theories which are partly attributable to his racist and misogynistic attitude. These characteristics result in his difficulty relating to other people. For example, he refuses to shake Poppy's hand when she tries to introduce herself. Scott is angered by Poppy's sunny personality and what he perceives as her lack of responsibility and concern for driving safety. He is exceptionally irritated by Poppy's choice of footwear (a pair of high-heeled boots) which he feels compromises her ability to drive properly. From the outset, Scott feels as if Poppy does not take her lessons seriously and is careless.
Scott, however, is not in a position to observe the behaviour which might belie his feelings about his new pupil. Poppy is devoted to her students, but her life isn't dominated by her vocation. She takes flamenco lessons with another teacher and a trampoline class (which leads to back problems and her being treated by an osteopath) and enjoys an occasional evening in the local pub.
At school, Poppy observes one of her pupils bullying his classmates. Rather than becoming angry with this student, she worries about him. A social worker, Tim, is brought in to handle the boy's case. Through Tim and the pupil's interactions, the latter reveals that his mother's boyfriend has been beating him. Tim and Poppy begin dating.
Poppy, Zoe, and Poppy's younger sister, Suzy, go to visit another sister, Helen, who lives with her husband in Southend-on-Sea and is pregnant. Helen proves to be an exceptionally judgemental person and tells Poppy that she needs to "take life seriously" and "not get drunk every night" and that she must plan for the future. Poppy responds that she is happy with her life as it is. In the ensuing scenes, Helen shows that she is a controlling individual who tries to dominate the lives of others. She thinks that she is better than everyone else and looks down her nose at people who do not think the same way that she does. For example, Zoe becomes cross with her when Helen will not let her husband and sisters play a game on the PlayStation.
Returning from the visit, Poppy observes Scott standing across the street from her flat, but he runs away when she calls his name. When she confronts him at the beginning of her next lesson, he insists adamantly he had been visiting his mother in Stevenage at the time she claims to have seen him. Scott drives erratically while ranting against other drivers and society. When he gives Poppy the keys to his car she tells him he is in no condition to give a driving lesson and she will drive him home. Scott demands that Poppy give him the keys back, tries to take them back by force, and then accuses Poppy of trying to seduce him in a long, rambling diatribe that makes it clear (at least to the viewer) that underneath his rage he has strong feelings for her. Unable to reason with him, Poppy waits until he has calmed down and then gives the keys back, telling him that the lesson will be their last.
The film ends with Poppy and Zoe rowing a boat in Regent's Park, as Poppy takes a mobile phone call from Tim and Zoe advises Poppy to think about "giving up being nice to everyone." Poppy dismisses the advice, cheerfully but not naively.