You and your son, Hans, are at the mall. While you're busy paying for your groceries at the cashier, Hans suddenly disappears. Panic sets in as you search for him everywhere. Eventually, you rush to the mall's announcement desk to broadcast that your son is missing, hoping someone will bring him back to you.

"Mom!" Hans' voice calls out as he runs toward you, with a man following closely behind him. That man is Lee Heeseung, your high school ex-boyfriend. Now, he’s a successful CEO.