A brutal series of murders point to a figure presumed dead for a decade. Detective Dong-geun arrives on a crime scene in a restroom and stumbles upon a diary fragment bearing a date from ten years past on the victim's body. Following the only lead he has, he discovers that the cryptic note is part of a diary belonging to Yeong-hun, a man who served alongside the victim during their military service but tragically took his own life a decade prior. Dong-geun suspects an executive at a pharmaceutical company who was implicated in military abuse in the past, but his investigation reaches a dead end when the man becomes the victim of a murder that followed the very same modus operandi. As suppressed memories resurface, the investigation takes an unexpected turn. 

Unforgivable is a film that delves into a serial murder case, all the while denouncing the harsh realities of military abuse and school violence—two pressing social issues in contemporary Korea. Co-director Lim Kyoung-ho crafted a gripping tale that goes beyond the conventional crime thriller, aiming to shed light on the seemingly words and actions that may be seen as thoughtless and insignificant but can linger in the victim’s memories and cause them great pains. In the lead role is the acclaimed actor Kim Jung-hyun, known for his versatile performances in popular TV series like Crash Landing on You and Mr. Queen.