In a province in Pusan, South Korea, the slow Yoon Do-joon is a young man overprotected by his mother that works with acupuncture and herbs and does not like his reckless army friend Jin-tae. When a Mercedes runs over Do-joon, Jin-tae follows the hit-and-run driver with Do-joon and find the car parked in a golf club. Jin-tae breaks the side mirror of the car and Do-joon collects golf balls lost in a lake. When they see the cart with the driver and passengers of the Mercedes, there is a fight and they end in the police station. During the night, Do-joon walks to the bar Manhattan to meet Jin-tae that does not arrive; when Do-joon returns home, he sees the Moon Ah-jung walking alone in an alley. On the next morning, Ah-jung is found dead on the terrace of a house. The incompetent detectives find a golf ball near her body and they conclude that Do-joon is the killer. Doo- joon is arrested; signs a confession and is charged of murder. However, his mother follows her instincts believing that her son is innocent and the scapegoat of the incompetent police department. The Mother investigates the truth with the help of Jin-tae. She finds Ah-jung was selling her body for food and liquor. She comes to know from a ragpicker that it was her son who accidentally murdered Ah-jung for calling him a retard. However, the police finds another mentally challenged person and puts the case on him. Knowing the dreadful reality, the mother flees the town in hopes of forgetting everything.