Ji Sung is a household appliances developer who dreams to live a life like a well-designed algorithm. While she was working on an AI refrigerator with voice recognition, a super sensor chip which National Intelligence Service lost, accidentally got assembled to Ji Sung's refrigerator and the "Ancestral Spirit" program that will tell who the scums are instead of the freshness of vegetables is born. Thanks to the program, Ji Sung finds out that her perfect elite fiance Jung Han was actually not her Prince Charming and despairs. One day, Gook Hee, a firefighter who the program couldn't analyze and knows nothing about social media, shows up. And Ji sung can't stop being skeptical about him. He has zero traces of his past on the internet. Who is he, and will he make Ji Sung despair again?