Yang Seungbae is a former investigator who has been demoted to patrolling police officer. As is noted by his superior, he appears to pry too much into investigations and trusts his (usually accurate) intuitions even when lacking evidence. Dutiful and prone to skepticism, he often second-guesses others' conclusions. These traits prove to be detrimental, as they cost him his position on the investigation team. Three years earlier, he had looked into the murder of Oh Sangwoo's parents. Though the case was declared cold, he investigated further and became suspicious of the assumption that the culprit was a burglar, finding the evidence of a break-in too convenient. This left him apprehensive of Sangwoo's character.