After awakening with a hangover, vain public relations agent Edina 'Eddie' Monsoon frantically prepares to launch a major fashion show. Meanwhile, her practical teenage daughter, Saffron—whom Edina had promised to quit drinking—constantly reprehends her mother's unhealthy habits. Edina's enabling best friend, Patricia 'Patsy' Stone, arrives to accompany her to work. At the office, Edina's hopelessly dimwitted personal assistant Bubble reports that one of the main models has dropped out.

Unable to fit into the majority of her clothes, Edina becomes determined to lose weight. At the office, she is horrified upon learning of an upcoming visit by Penny Caspar-Morse, a thin model that used to torment Edina about her weight. Edina unsuccessfully attempts to exercise, and with Penny arriving earlier than expected, she accepts Patsy's suggestion to undergo a liposuction.

Edina and Patsy holiday in France, where they find themselves staying in a rustic cottage, rather than the château they were expecting. There is no food or wine, and the duo are constantly disturbed by an old man whose French they cannot understand. They're later rescued by Saffy, who arrives with supplies, and Bubble, who tags along to deliver an urgent message concerning Edina's home decorating business, but she forgets about it.

Patsy helps Edina break in her new isolation tank upstairs, while Saffy works with classmates on a presentation for her sixth form college's open day. Edina, feeling useless after a newly dedicated and proficient Bubble hauls charge of the office, takes a sudden interest in her daughter's work and begs to be invited to the open day. Saffy vehemently refuses, so Edina spitefully threatens to adopt a Romanian orphan.

Edina is none too pleased about her fortieth birthday. As opposed to the glamourous, star-studded surprise party she had hoped for, Edina is disappointed to learn that Saffy has planned a quiet lunch with family and friends—including both of Edina's ex-husbands, Justin and Marshall, and their respective new lovers, Oliver and Bo, as well as Patsy and Mother.

Patsy, temporarily staying with the Monsoons, becomes jealous when Edina reconnects with an old boyfriend. During one of her infrequent appearances at work, Patsy is assigned to host a fashion makeover segment on a morning programme. After clashing with the models, Patsy persuades Saffy and Mother to appear in their place, telling a tale of her emotionally distant mother as psychological manipulation.