Kassie Singleton (Jennifer Aniston) decides she wants to have a baby. Despite the objections of her neurotic best friend Wally (Jason Bateman), she chooses to do it alone, with the services of handsome and charming sperm donor Roland (Patrick Wilson). Wally has always had feelings for Kassie, but as his friend (Jeff Goldblum) points out, he missed his chance and she put him in the "friend zone". But things don't go to plan, as Wally gets so drunk at Kassie's "insemination party" that he accidentally spills Roland's semen and replaces it with his own. Seven years later, Kassie returns to New York along with precocious-but-neurotic son Sebastian (Thomas Robinson). Wally forms a bond with this loveable mini-version of himself, but the bad news is that Roland is in the picture too.