High school student Yoshiro Kobayashi (Mahiro Takasugi) is the great-grandchild of the first president of the Boy Detectives Club. He enjoys time with his friends Watari (Gaku Sano) and Saya (Mayu Hotta). One day, the Fiend with Twenty Faces appears in front of Yoshiro. Mysterious cases then takes place in sequence.

Nanase Sakura is a 23-year-old rookie nurse. She met Dr. Kairi Tendo several years ago and fell in love with him. To meet him again, she studied hard and became a nurse. After 5 years, she finally meets Tendo again, but he has a totally different personality than what she imagined. Tendo, who is 31-years-old, is commonly referred to as the "Devil" at work. He is a level-headed perfectionist and often makes biting remarks to doctors and nurses. Nanase works hard to receive recognition from Tendo and she also expresses her feelings honestly to him. Due to her persistence, Nanase becomes well known at the hospital and she picks up the nickname of the "Warrior." Meanwhile, Tendo becomes attracted to Nanase.