A young psychiatrist name Jung Byung Hee enjoys helping many patients, and starts a new life by making weekly visits to homes in need of help for free. One day, he gets a call from a woman, stating that a young lady by the name of Lee Yejin is suffering with a mental disorder called Posttraumatic Stress Disorder (PTSD). This disorder causes Yejin to fear people, because of past experiences. 

Byung Hee promises that he'll chagne Yejin by 31 one days, which is almost impossible for her case.