When a fire broke out in the Mitarai household 13 years ago, the eldest daughter, Anzu, had to watch her mother, Satsuki, grovel to the ground and beg for forgiveness, as she thought it was her fault. Things only went downhill for the family, with Anzu's parents divorcing shortly after the incident.

Living with her younger sister Yuzu, 25-year-old Anzu—now surnamed Murata—works at a house cleaning company to pay for Satsuki's hospital bills. Her newest client is Makiko Mitarai, the second wife of Anzu's father who presents herself as the perfect housewife when, in reality, she refuses to clean any mess.

Having always believed Mikako was the true instigator behind the fire, Anzu considers this the ideal opportunity to prove her mother's innocence. Under the alias "Shizuka Yamauchi," she plans to infiltrate Mikako's house and search for evidence that will determine her culpability. Nevertheless, Anzu must remain cautious if she wants to succeed, as a single wrong step might prove too costly.