Lee Ahn and Jin Yeong have been in an on-and-off relationship for nine years since they met in college. One day, Jin Yeong breaks up with Lee Ahn. Even before Lee Ahn becomes used to her single life, she hears the news of her ex-boyfriend’s death. Jin Yeong’s cell phone is transferred to Lee Ahn according to his will, but the phone is locked. If Lee Ahn enters the wrong password for the 10th time, the phone will get reset and all of Jin Yeong’s memories will be deleted forever. While Lee Ahn is still struggling to accept her ex-boyfriend’s death, a guy called Jin Yeong joins her company. His name and habits remind Lee Ahn of her deceased ex-boyfriend, bringing back old memories of him. Ahn starts to enter passwords, recollecting old memories. Will she be able to reach Jin Yeong’s memories within 10 tries?