Kevin Burke is a college professor and single father, who believes there is a scientific explanation for everything - except how to control his scheming pre-teen daughters. Mary-Kate and Ashley Olsen are twin sisters, who are complete opposites: Mary-Kate is a tomboy, whose biggest interest is perfecting her jumpshot and her curveball; Ashley is a straight-A student, who dreams of a modeling career and boys. And then there's Carrie, a 26-year-old freshman in Kevin's class, who has come late to college after exploring the world. Carrie is quirky, difficult, beautiful, and quick to speak her mind, so when she answers Kevin's ad for a part-time nanny for the girls, he is convinced she's nothing but trouble. The girls think she is a dream-sitter come true, and agree to put their differences aside to join forces to make a little chemistry between their by-the-book father and the beautiful woman who seems to drive him crazy in all the right ways.