Although she just lost her mobile phone

On the way home from get off work, Nami (played by Cheon Yuhi) lost her smartphone, which contained all her personal information. Joon-young (played by Im Si-wan) finds Na-mi's phone and returns it to her, but has spyware installed inside it. By following her daily life, he learns everything about Nami—her whereabouts, hobbies, tastes, work life, finances, and social networks—and gets close to her by hiding his true identity. At the same time, detective Ji Wan (played by Kim Hee Won) discovered traces of his son Joon Young at the murder scene, so he launched a secret investigation into him and prepared for the worst. Nami was relieved to find her phone, but it wasn't long before her daily routine was turned upside down. Just because she lost her cell phone, her entire life was in jeopardy.