Contains spoilers for this episode.
Mia helps Rob hide a cyclist's body after he kills the man while driving drunk. Years later she has a family and a successful career as an architect. Rob reappears at her hotel, sober and planning to write to the victim's wife. Fearing what his confession could cost her, Mia kills him. While dealing with his body, she witnesses a delivery vehicle strike a pedestrian outside.
Insurance investigator Shazia examines that separate accident using a machine that displays witnesses' memories. Music and smells help people recall the street, gradually leading her toward Mia's hotel window. Mia tries to rehearse an innocent account, but the scan exposes both killings. Shazia promises confidentiality and attempts to leave. Mia stops her, takes her captive and uses the same equipment to discover whether anybody knows where the investigator has gone.
Shazia's memory reveals that she told her husband about the visit. Mia murders her and drives to the family home, where she kills the husband and their infant son to eliminate witnesses. She then joins her own family at her son's school performance. Police discover that the baby was blind, making that murder especially pointless. A guinea pig in the room did see what happened, and its memories provide another route to the killer. Officers arrive at the school while Mia sits among the applauding parents.