Edina enrolls in a boot-camp fitness programme and subjects herself to a strict diet, after being ridiculed for her weight by Katy Grin, Catriona and Fleur. Meanwhile, Patsy briefly experiments with pulling back her signature fringe for the first time in decades, and budding playwright Saffron receives a visit from Taylor, a pretentious old school friend with acting aspirations. Despite initially struggling, Edina's efforts soon pay off as she realises she has lost one stone. Proudly displaying her slimmer figure, Edina meets her friends again for lunch, but her weight loss is still not enough to deter Katy Grin's snide remarks.

Edina decides to rent out her house to Michael Douglas during the Summer Olympics, hoping it will lead to prestigious A-list parties, even though Patsy—who now needs incontinence pants—no longer shares Edina's penchant for partying. However, Bo and Marshall arrive instead, after Michael gave the couple his party invitations. Frustrated with her dwindling social life, Edina happens upon one of Michael's invitations, allowing her and Patsy to attend a pre-Olympics party. The pair are eventually escorted out after Edina harasses Stella McCartney.

After awakening with a hangover, Edina 'Eddie' Monsoon frantically prepares to launch a major fashion show. Meanwhile, her unsympathetic daughter, Saffron—whom Edina had promised to quit drinking—constantly reprehends her mother's unhealthy habits. Edina's best friend, Patricia 'Patsy' Stone, arrives to accompany her to work. At the office, Edina's assistant Bubble reports that one of the main models, Yasmin Le Bon, has dropped out, while Princess Anne has replaced Princess Diana on the guest list. Edina subsequently manages to cajole several B-list celebrities into attendance, turning the show into a rousing success. Later that night, Edina and Patsy indulge in a drunken bender—much to the disgust of Saffron, who locks Edina out of the house. The next morning, Edina and Patsy trick Saffron into believing that Edina is going to check into a rehabilitation clinic.

Edina decides to remodel the kitchen again, and calls up her old minimalist friends. It turns out Bettina is divorced and is clinically insane and Max is revealed to be gay. Bettina transforms the kitchen into a stairless white box, but Edina hates it. Patsy, meanwhile, develops serious health problems and walks around with an IV stand. Saffron returns from her wedding to John in Kenya and reveals that he is a polygamist. Edina and Patsy head off to meet designers Terence Conran and Kunz for inspiration. At Kunz's store, Edina claims to have seen her ideal kitchen in a previous life, so she hires a channeller. The channelling session results in so much disruption in the household that Saffron and Edina argue once again, and Edina lashes out at baby Jane in anger. Saffron has finally reached breaking point, and kicks Edina and Patsy out of the house, which is in her name. Edina and Patsy end up lounging in the stylish window display of Terence Conran's Shop.

Edina is left feeling helpless after Saffron leaves home to attend university. Patsy loses her job when Ella magazine folds; she later receives an offer to work with her colleague Magda at a New York magazine. Edina and Patsy commiserate drunkenly with each other over old age and the sudden changes in their lives. Saffron returns for a visit, appalled at their behaviour. When Edina announces plans to sell the house before embarking on a journey of self-discovery, a livid Saffron storms off. Edina's plans also mean that she is cutting off Patsy. Embittered, Patsy leaves as she decides to take the job in New York.

When Saffron hires a handsome landscape gardener to redesign the backyard, Patsy recognises him as Jago Balfour, the younger brother of a wealthy acquaintance of hers, who inherited a country estate before dying of an overdose. Presuming Jago to be rich as well, Patsy goads Edina into seducing him. Edina and Jago soon arrange a dinner date, which eventually leads to a wild night of lovemaking. The next morning, Jago reveals that his brother squandered the family fortune on drugs, forcing him to sell the estate to Roger Daltrey as a fish farm, much to the horror of Edina and Patsy.

Edina's home is a mess, and she has done some more remodelling as usual. The changes include a pool in her bathroom, and a shower that washes and buffs her like a car wash. Her new client Emma Bunton comes by to discuss new jobs. It turns out Saffron was Emma's head girl at school and Emma knows that Saffron would be disturbed by Edina's squalid house. When they realise that Saffron is coming home that day from volunteer work in Africa, Emma urges everyone to clean up. Patsy gets obsessed by organising a drawer full of odds and ends. When Saffron arrives, Edina taunts Saffron for becoming fat and fulfilling her "genetic fate." Saffron informs her that she is not fat, she is pregnant. Edina tells Saffron that she should tell people that she is pregnant right away or people will think she is fat.

Edina begins an ad campaign for Prince Charles' biscuits, and claims that it is "by royal appointment". she begins to associate with the wealthy socialite crowd, and buys a weekend at a country house hotel. Upon arrival, Patsy and Edina discover that nothing is in season, and the place doesn't even have any jacuzzis or massage. Patsy tells Edina that the Rothschilds were laughing at her. Edina becomes angry and determines that she will kill something, and goes out with Patsy with guns blazing in the middle of the night. They bring a pheasant back to the hotel, which Edina puts in the closet. In the morning they discover that the pheasant is still alive. Patsy tells Edina to pull its neck but Edina bonds with it and drugs it and releases it into Hyde Park. At home, Emma and Sarah bring gifts to Saffron for a baby shower, and Sarah becomes obsessed with Emma. Sarah stalks Emma, and Saffron eventually calls the police and has Sarah arrested.

Patsy has booked Saffron's baby Jane (Lola) for a photo shoot with Jean-Paul Gaultier. Gran usually babysits Jane on Thursdays, so that Saffron can go out with John. But Gran does not come this Thursday, because Edina has banned her from the house. So Saffron and John are stuck at home, and Patsy can not take the baby to the photo shoot. Patsy and Edina prey on Saffron's insecurities and tell her that John will lose interest in her, Saffron bursts into tears and agrees and asks Edina to look after Jane while she goes out with John. Edina and Patsy plan to take the baby to have a photo shoot at the London Zoo. Saffron returns and finds out they took the baby out against her wishes and Edina explains that she has bonded with Jane, however it is later discovered that Edina has brought home the wrong baby.

Edina, who now runs a television production company, is slated to make a guest appearance with client Twiggy on Richard and Judy's morning television show. Patsy has been injecting her face with Parralox, a Botox-like substance, in order to freeze her wrinkles. Edina is persuaded by Patsy to try Parralox as well, but she awakens the next morning with a paralysed face. In addition to costing Saffron a government job, Edina is replaced by Katy Grin, her new business partner and Bubble's cousin, for the television appearance.

Saffron is preparing her home birth kit. She's due to have the baby anytime, Patsy is the hostess of the Style Awards at the Royal Albert Hall. Edina helps Patsy rehearse her speech but is interrupted by Katy Grin, Bo, and Marshall. Katy talks about her work in the musical Chicago. Bo and Marshall talk about their Christian Family Creation adoption service, which is a service for busy Hollywood actresses who have no time or desire for pregnancy. Saffron and Patsy shove each other trying to get up the stairs, and then suddenly Saffron's waters break, spilling baby juice all over Patsy's expensive clothing. Saffron retreats to her bedroom with contractions. In a rare moment of support for her daughter, Edina tells Patsy she won't be able to go to the awards show. Saffron eventually gives birth to a healthy baby girl.

Edina's 'new' boyfriend Pete is a tape engineer who used to work at Abbey Road Studios during the time that the Beatles recorded there, and who had found some unreleased tapes. In a studio, the girls have fun and Edina sings her 'walking down the road' song she loves. There are flashbacks from the sixties where Patsy is a man and they are at a recording for the Sgt. Pepper album. Back at home, Elton John had been invited to the party to debut the Beatles tapes, but gets annoyed and leaves when he discovers he was only invited to play piano in the background. Finally, just after proposing marriage to Edina, Pete plays the tapes at the party. Instead of The Beatles, Edina is heard singing. Apparently this is because Patsy had pressed the record button on the recorder in the studio by mistake whilst she was looking for champagne in the control room, and Edina unknowingly sang over the tapes.

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. After a disturbing nightmare about the procedure going horrifically wrong, Edina decides against the idea and instead puts on an oversized sweatshirt in order to cover herself up. Patsy announces that Penny is blind, much to Edina's delight. Later, Edina drunkenly rants at Penny about how she ruined her life and brags about how successful and thin she has become. However, she inadvertently reveals her weight as she grabs Penny's hands and places them on her waist.

Edina frantically organises her cluttered house in order to host old friends Bettina and Max, who were once obsessed with minimalism. Feeling ignored by Edina, Patsy leaves in search of another lunch partner. When Bettina and Max arrive, Edina is disappointed to learn that they are now the hysterical, neurotic parents of a newborn baby. As the couple wreak havoc, Edina quickly leaves the house. At a restaurant, Edina and Patsy compete against each other by attempting to befriend famous people: Patsy invites herself to lunch with Britt Ekland and Zandra Rhodes, while Edina forces her client Lulu to have lunch with her. Both lunches end awkwardly. Back home, while Saffron and Mother comfort Bettina, they hear Edina and Max having sex over the baby monitor. After the couple finally leave the intended result of Edina's fling she and Patsy make peace.

Bubble accidentally emails Edina's clients' details to nemesis Claudia Bing, who poaches most of Edina's clients, including Twiggy. Patsy—who has recently been diagnosed with osteoporosis—and Edina are horrified when Saffron forces them to attend a Menopausals Anonymous meeting organised by her. In order to save her business, Edina dupes Claudia into buying her TV company—which currently has no programmes—while Claudia also agrees to return several high-profile clients. Saffron has a terrifying nightmare in which Patsy threatens to impregnate herself with a vial of Mick Jagger's sperm unless she is allowed to move into the spare room.

Edina has a nightmare about Saffron's baby trying to stab her. It turns out that the face of the nightmare baby belongs to Saffron's midwife, who delights in teasing Edina about these nightmares. Edina expresses her displeasure about this baby. Saffron invites the father of the baby to the house to tell him she is pregnant. In the meantime, Edina and Patsy have organised a book club, but no one is interested in reading any books except celebrity magazines. When Edina discovers that John Johnson, the father of Saffron's baby is black, she is overjoyed, because she thinks a mixed-race baby is the greatest accessory, the "Chanel of babies." When Saffron tells John that she is pregnant, he replies that she should tell people that she is pregnant right away or people will think she is fat.

Patsy, who is temporarily staying with the Monsoons, becomes jealous when Edina reconnects with an old boyfriend. During one of her sporadic appearances at work, Patsy is assigned to host a fashion makeover segment on a morning television show. After clashing with the models, Patsy attempts to persuade Saffron and Mother to appear on the show in their place, telling a tale of her emotionally distant mother. Saffron agrees, on the condition that Patsy moves out of the house and does not interfere with Edina's relationship. Patsy's television appearance turns disastrous as she suddenly becomes nervous. After Patsy convinces Edina to break up with her boyfriend, Saffron lashes out at Patsy for not upholding her end of the deal.

Edina becomes frustrated when she loses a prestigious PR award to rival Claudia Bing, despite having bribed the judges. Worried about her dwindling career, Edina works on a campaign in hopes of upstaging Claudia. Meanwhile, Saffron becomes romantically involved with Gerard, her psychology lecturer, until she discovers that he is married with children. In a rare occurrence, Edina comes to Saffron's aid by punching Gerard in the face. At an industry luncheon, Edina's speech is stolen, prompting a drunken rant against the bastardisation of the PR industry, which proves a success. When Edina and Patsy attempt to retrieve the speech, the duo awaken the next morning on a trash barge headed for Ostend.

Edina joins a New Age commune, but she struggles to fit in and quickly becomes bored. Patsy finds herself disillusioned with her new job in New York due to creative differences with her co-workers. Saffron settles into university life and Mother spends her days at the Monsoon house, drinking champagne and ordering items from the shopping channel. After realising that their lives are not the same without each other, Edina and Patsy happily reunite on top of Carnegie Hall Tower before returning to London. Back home, Mother has been arrested for squatting and credit card fraud. A flashforward to 25 years into the future provides a glimpse into the lives of Edina, Patsy, Saffron and Mother.

Patsy is excited to be joining young supermodel Erin O'Connor for a magazine photo shoot in Paris. Edina and a reluctant Saffron come along for a mother–daughter fashion spread. After learning that other models from her generation will also appear in the shoot, Patsy becomes competitive and constantly ignores the photographer's directions, much to his annoyance. Meanwhile, Edina and Saffron spend an unusually pleasant day together in Paris, going shopping and dining at upscale restaurants. Edina later encourages Saffron to flash her breasts from the top of the Eiffel Tower. However, Edina's ulterior motive is revealed when a photographer appears unexpectedly and takes a topless picture of Saffron for a magazine.

For the first time ever, Edina has agreed to stay home and spend Christmas with the family. Edina typically goes overboard by buying a huge tree and tons of gifts. Patsy is very upset that she cannot go away on vacation with Edina as they do every year, as she hates Christmas. Patsy has a flashback of unpleasant Christmas memories of her childhood. Someone somewhere sticks a pin in a Patsy voodoo doll, and she collapses in pain beneath the Christmas tree. Although Edina and Saffron ignore her, John insists that Patsy needs to go to the hospital. Once at the hospital, the doctors tell Edina that Patsy is very sick and that she may die. Edina and Saffron return to the house to continue their Christmas celebration. In the middle of the night, Patsy's estranged sister Jackie arrives to visit her. The following day, Edina and Saffron drop by only to learn from a nurse that Patsy has died, only they find out that it turns out to be Jackie instead.

When Saffron berates Edina for being lazy and incompetent, Edina and Patsy decide to impress her by booking her favourite French film star, Jeanne Durand, to perform at the Royal Albert Hall. However, they are dismayed when Jeanne refuses to sing aloud and instead merely mouths the lyrics. As a solution, Jeanne lip-syncs to Bubble's vocals on the night of the concert.

Patsy helps Edina break in her new isolation tank upstairs, while Saffron works with classmates on a presentation for her sixth form college's open day. Edina is left feeling useless after Bubble, now a dedicated professional, takes charge of the office. She takes a sudden interest in Saffron's presentation and begs to be invited to the open day. When Saffron vehemently refuses, Edina throws a tantrum and threatens to adopt a Romanian orphan—to the point of instructing Bubble to send over a selection of babies so she can pick one. She then frantically tries to cancel the deal, but it is too late. Saffron eventually allows Edina to attend the open day. However, the presentation is interrupted as the babies arrive and start wailing, angering Saffron. Edina then wakes up in a panic, still in her isolation tank, and realises it was all a dream.

Edina is none too pleased about her 40th birthday. As opposed to the glamorous, star-studded surprise party she had hoped for, Edina is disappointed to learn that Saffron 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. Edina behaves erratically during the party, switching between self-pity and spite, and she soon provokes Oliver, her least favourite guest, into making an angry exit. Justin and Marshall are shocked to discover that they have both been paying alimony to Edina. While Edina and Patsy sing drunkenly on a new karaoke machine, Justin and Bo secretly plot to cut off Edina's alimony.

Edina and Patsy travel to Marrakech for a photo shoot. They are accompanied by Saffron, who is interested in studying the local indigenous peoples for school. There, Edina and Patsy meet up with an old friend, Humphrey, who sexually harasses Saffron. At dinner, it is revealed that in the 1970s, Patsy spent a year living as a man until "it fell off", according to Edina. The following day, during a shopping trip to an outdoor bazaar, a spiteful Patsy decides to sell Saffron to white slavers. Edina and Patsy later go to the photo shoot location, but when no one shows up, they end up lost in the desert. After wandering around for a day or two, the pair are rescued as they stumble upon Saffron, who is wearing a burqa. They spend the last few days of their trip drugged and unconscious, while it is implied that Saffron had a secret dalliance with Humphrey's houseboy.