Doo-sik (Jung Jun-ho), the second-in-command of a top gang, Dogs D, full of ambition and expectations, finds himself with the opportunity to return to school, not as a student but as a teacher. This is truly something unexpected for him, as he never completed his high school education many years ago. Now it’s a second chance for him. He only justifies taking up this teaching profession as something like a social adaptation course for prisoners who will be released and reintegrated into society soon. But does he have what it takes to be a teacher? Even on the first day, he stands out and appears eccentric. He enters the school through a dog hole. It will take a while for him to realize that his behavior is just too much for the students to accept and respect in a teacher. And when fate will have it, his own boss, the leader of Dogs D, is right in front of him, as one of the students, and his two loyal men are always out of reach whenever he faces trouble! Doo-sik just rushes here and there, and all the incidents are leading Doo-sik to an unexpected place.