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.

Patsy becomes the subject of a tabloid sex scandal following an affair with a married MP. Edina checks into a hospital for surgery after injuring her big toe. Patsy tags along, planning to undergo a chemical peel in preparation for her interview with Hello! magazine. While anesthetised, Edina dreams that she is on her deathbed, surrounded by idealised versions of family and friends, while Patsy envisions herself looking young for her Hello! spread. Edina awakens to find that her pains were caused by a stray acupuncture needle that worked its way from her cranium to her toe. Meanwhile, a botched facelift leaves Patsy's face covered in burns. The Hello! spread is also a disaster, with the article reporting Patsy's age as 49, blaming her for the sex scandal and revealing her horrific facelift.

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.

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.

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'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'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.

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.