Mollie, an accountant living in New York City, becomes pregnant during an affair with married executive Albert. The baby, while growing inside Mollie, begins to make voice-over commentary. In her ninth month, while out shopping, Mollie and her friend Rona catch Albert with another woman, and Albert admits he does not plan to stay with Mollie. The heartbreak and stress cause Mollie to go into labor. A taxi driver speeds through downtown traffic to get her to the hospital in time. Mollie becomes a dedicated single mother and Mikey continues his commentary, using an "inner voice" which can also communicate with other babies.She meets the taxi driver, James, again at her apartment building. Over the course of the next year, the two develop a friendship and tentative romantic relationship. James tells Mollie that he loves her, but she says she only wants what is best for Mikey, that rushing into things is how she got into trouble, and kicks him out. Mollie is forced by her boss to continue working with Albert, which complicates matters further. At the playground, Mikey is told by his friends what "daddies" are and he realizes he wants James to be his father.James comes to the apartment and tells Mikey that he will not be around any more, and Mollie listens over the baby monitor as he pours his heart out to Mikey, who admits he will miss James, too. Mollie takes Mikey to Albert's office to meet him, but when Albert admits he does not want the responsibility of being a father because he's going through a "selfish phase", Mollie realizes he has not changed. She leaves Albert behind for good and makes up with James.Meanwhile, Mikey wanders off on his own, searching for James when he sees a taxi cab outside. After making his way out to the alley, he gets into a car which then gets towed away with Mikey inside it, while Mollie and James search frantically for him. After spotting him, James and Mollie give chase in his cab and eventually cut off the tow truck, but discover Mikey had gotten out of the car and is now standing in the middle of heavy traffic. James and Mollie run to reach him and take him to safety, where Mikey unofficially asks James to be his father by saying his first word "Da-da". James and Mollie realize that Mikey already sees James as his father, and they decide to give it a chance, kissing passionately while Mikey considers telling them he needs a new diaper.Nine months later, Mollie gives birth to her and James' daughter and Mikey's half-sister Julie, complete with her own inner voice.