Tinker Ticker: Park Jung-gu sends out homemade bombs to people he finds online who are likely to use them, yet these devices are unused. One day, Jung-gu meets Lee Hyo-min, a delinquent student at his university and sends him a package. Soon an explosion in a delivery truck hits the news. Before long, Hyo-min discovers who is sending him the packages and the two form a tenuous relationship. However, Hyo-min's unpredictable behavior becomes dangerous and Jung-gu finds himself caught in a situation that he can no longer handle.