A movie about the damage caused by the humidifier disinfectant disaster. It reveals the truth of the mysterious deaths of victims without perpetrators, and informs the world of the pain of the victims and their bereaved families, which is still ongoing. An elite doctor Taehun (Kim Sangkyung) finds out that his six-year-old son has an unknown lung disease. While he’s suffering from his son's sudden illness, even his wife (Seo Younghee) suddenly dies. Taehun learns that his wife, who had been healthy, suddenly died of lung disease and begins to find out the reason as a doctor. He starts to dig into a huge secret of the case, investigating the cases of the people who died of similar symptoms with a prosecutor Youngju (Lee Sunbin), the younger sister of his deceased wife.