After murdering his wife he comes across old classmate Jong-suk, who he hasn't seen for 15 years.
Over dinner, they look back on their school days, when the rich elite students "The Dogs" cruelly bullied "The Pigs," their weaker and poorer peers.
They were powerless against the bullies until one of their fellow students Kim Chul adopted the role of hero to break the cycle of fear.
The two return to their old school where a shocking truth is revealed which underpins this gripping analysis of class inequality and gang hierarchies. It's an outstanding work of animation for adults.