The actress' alter-ego, Charlotte York Goldenblatt, is convinced spouse Harry is having an affair so she and the couple's two young daughters, Lily and Rose, move out of their luxury apartment in Manhattan's Park Avenue.
However, it turns out Charlotte is mistaken and Harry is actually sneakily seeing a contractor, who is building a dream home for Charlotte as a surprise.
Despite Charlotte's accusations, the couple soon reunite.
In the movie, Charlotte and Harry also let Carrie Bradshaw - portrayed by Sarah Jessica Parker - and husband Big move in with them when they lose a huge amount of cash in the recession.
Big - played by Chris Noth - eventually travels to the Middle East to try and recover their fortune.
Cynthia Nixon's character, Miranda Hobbs, makes a life-changing decision when she leaves her career as a lawyer after being sued for malpractice and opens a restaurant with husband Steve.
It is also thought Carrie's gay best friend Stanford Blatch will marry camp wedding planner Anthony Marentino, with Liza Minnelli making a cameo singing at their reception.
A source said: "All signs point to a gay union between Stanford and Anthony Marentino, who's required to wear a black tuxedo in the scene. Slated as the entertainment: Liza Minnelli."
The highly-anticipated movie is due out next May.
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