Marlo is a New York suburbanite who's about to give birth to her third child. Her husband, Ron, is loving and works hard, but remains clueless about the demands that motherhood puts on his wife. When the baby is born, Marlo's wealthy brother hires a nighttime nanny named Tully to help his sister handle the workload. Hesitant at first, Marlo soon learns to appreciate all that Tully does -- forming a special bond with her new, lifesaving friend.