Chuck learns more about Sarah's past. But when they run into her old high school nemesis Heather Chandler, Sarah's insecurities come to the surface and she tries to avoid Heather. Chuck does everything he can to hear more about Sarah's life. When Heather's husband Mark turns out to be a key player in the next mission, the agents must go to Sarah's high school reunion to prevent the sale of dangerous super-bomber plans. Meanwhile, Big Mike leaves town and Lester decides to implement a new policy.