A grieving father seeks to understand the circumstances that led his teenage son, Ki-tae, to commit suicide. The discovery of a photo prompts him to seek out the young man's friends, Dong-yoon and Hee-june. Before viewers' eyes, a complex picture of the dynamic between them develops - friends and foes-bullies and victims-brothers and strangers. What could have pushed the bond between the three young men past its breaking point?