Overview: On her way home from work, Na-mi (Chun Woo-hee) loses her smartphone, containing everything about her. Jun-yeong (Yim Si-wan) finds Na-mi’s phone and returns it to her, but after installing spyware. By tracking her everyday life, he learns all he can about Na-mi — her whereabouts, hobbies, tastes, work life, finances, and social network — and approaches her by concealing his true identity. In the meantime, police detective Ji-man (Kim Hie-won) finds traces of his son Jun-yeong at a murder crime scene and secretly investigates Jun-yeong, suspecting the worst. Na-mi is relieved to have found her phone, but not too long, her ordinary life turns upside down and spirals out of control. All because she only lost her phone, her entire life is imperiled.