A girl is found dead in the swimming pool in her house. The cause of death is determined to be heart attack, and police rules the death natural. However, Utsumi spots a purple mark on the victim's chest, and asks the coroner to analyze it. It is revealed to be necrosis, which prompts Utsumi to consider the girl's death suspicious. It is later revealed that two more victims have died under the same circumstance, which strengthens Utsumi's belief that this is a homicide case.