Tae-kyu (Kim Kang-woo) is a former professional baseball player who currently coaches for a minor league team. His girlfriend Joo-young (Kim Hyo-jin) runs a successful urology clinic. They've broken up once before then gotten back together, and now they're about to get married. But a week before their wedding, Tae-kyu learns something about Joo-young that makes him feel betrayed and jealous. Growing increasingly neurotic, he becomes obsessed with finding all about her exes and dating past.