Lee Na-Mi (Chun Woo-Hee) works as a marketer at a start-up company. She is an ordinary office worker who works hard everyday. On a fateful day, Lee Na-Mi loses her smartphone, but she luckily gets her phone back. Since that time, her ordinary peaceful day are threatened. Oh Jun-Yeong (Im Si-Wan) happens to pick up Lee Na-Mi’s smartphone. Oh Jun-Yeong , who approaches Lee Na-Mi by using her smartphone, commits crimes using smartphones.
Meanwhile, Detective Woo Ji-Man (Kim Hee-Won) investigates a murder case involving a dead body that was found on a remote mountain. There, he finds clues that points to his son Woo Jun-Yeong as the possible perpetrator.