Carrie finds out that her building is going co-op and she has to move. Aidan offers to buy her apartment and move in with her. Carrie finds herself both tempted and scared about the idea of sharing her space on a permanent basis. She's even more alarmed when while rummaging through Aidan's clothes she lands upon an engagement ring. It's creates such an internal upheaval, she runs to the kitchen sink and vomits. Carrie tells the girls about her reaction and voices her fears that it's too fast ? and that to boot, the ring is not at all her style. Miranda admits that she had helped Aidan select the ring. Carrie nervously waits for Aidan to pop the question and wonders: How do you know when it's right?
Meanwhile, Samantha has a drink with her new client, Richard Wright. He proudly tells her that he enjoys sleeping around and is not at all interested in marriage, piquing single-girl Samantha's interest. Their next encounter finds them in Richard's private jet headed for the mile-high club.
Miranda tells Steve that she's carrying his baby and is going to keep it. Steve is shocked, especially when Miranda tells him she's going to take care of the baby herself. Meanwhile, fertility challenged Charlotte starts taking hormones and learning Chinese in case they need to adopt a Mandarin baby.
Carrie runs into Big and tells him that Aidan wants to marry her. Big tells her that Aidan's not the man for her and that she's not the marrying kind. Carrie replies that she's just not ready.
At the annual Highland Fling, Bunny tells Charlotte that a Mandarin child is out of the question for the MacDougal clan. Charlotte screams at Trey and rushes home. Later, when Charlotte asks Trey for her hormone injection, Trey admits that he is having second thoughts about having a baby. He says he doesn't want to try anymore and wants it to be just the two of them.
Aidan proposes to Carrie as they take Pete for his nightly walk. The ring he gives her isn't the one Carrie had spotted; it's beautiful. After Aidan tells her he wants to spend the rest of his life with her, Carrie takes a deep breath and says yes.
Across town, Miranda opens her door to Steve who is holding out an engagement ring. Miranda tells him he's crazy and they both agree they don't want to marry each other. They decide they'll figure things out.
Carrie tells Samantha she's engaged and shows off her ring. Samantha orders them a drink and tells her that she picked the ring out with Aidan.