In the past few years, Emma Stone — the smiling Circe of the green eyes, sultry voice and fetching overbite — has been pursued by zombies (Zombieland) and Jonah Hill (Superbad). In her first shot at a lead, she plays a nice, bright high school girl who pretends she had sex with a college guy and, as the rumor spreads, quickly gains a notorious rep. A breezy update of The Scarlet Letter, the film is an O.K. entry in the subgenre of smarty-pants comedies about young love, like Nick and Norah's Infinite Playlist and (500) Days of Summer. To this mild enterprise, Stone lends winning maturity and a gift for making sassy dialogue sound natural. This 22-year-old is an actress-personality — a star — around whom Hollywood could build some pretty good movies. Katherine Heigl, watch your back.