Tae-sik (Kim Rae-won) dropped out of high school and became a gangster. Every time he got drunk and started a fight, he would fight without reservation, and even get braver and braver when the fight was intense, so everyone gave him the nickname Mad Dog. But Tae-sik was later imprisoned, and he seemed to have become a different person when he was released on parole. His attitude of turning a blind eye to his enemies made everyone very confused. He carried a manual with him all day long, which originally recorded the ordinary things he had to do in his life. This was the manual he recorded in prison. He wanted to set three rules for himself and make himself better. The manual was given to him by Deok-ja, and he found this old man on purpose. Deok-ja treated Tae-sik as if he were his own son. But Deok-ja's daughter Hee-soo always spoke ill of Tae-sik, but in fact she didn't hate Tae-sik. The three of them were about to start their new life, but no one believed that Tae-sik was willing to change himself.