 When Carrie s apartment is going coop, Aidan proposes to buy it together. She finds a ring in his things, and accidentally insults Miranda who helped pick it out. Trey s MD tries to control Charlotte s reproductive zeal in light of the tough statistics of in vitro fertilization, but at the annual Highland Fling Bunny s objection to a  mandarin granddaughter  causes a marital row. Samantha finds out Richard Wright is a though boss but into quick sexy without commitment, such as a flight to Rio. Miranda tells Steve he becomes a father but she doesn t expect his help.