Now that Lizzie Sellers is twenty-one, Nic Maretti can't think of a single reason why he has to stay away from her any longer. When he sees her again at Stefan and Jen's wedding, he decides he wants her. And what Nic wants, Nic gets. He just gets a whole lot more than he bargained for with Lizzie. Lizzie Sellers has had a crush on Nic since she was seventeen. Now that she's started a doctoral program in theoretical math, she decides it's time to put away childish things so she can focus on millennium prizes and solving one of the world's unsolvable problems. So when she sees Nic at Jen and Stefan's wedding she decides it's the perfect opportunity to get him out of her system. There is no way the real Nic Maretti could ever live up to the fantasy she's created over the years. Except Lizzie finds out quickly that solving her Nic problem may be even more impossible than solving the Riemann Hypothesis. And sometimes reality is way better than fantasy. What happens when two people who have already made up their minds what the rest of their lives looks like discover an even better solution that is at once terrifying and irresistible?