Kim Ji-su, a hotel cleaner, has a secret ability: she can read people’s hidden truths through the “stains of memory” left behind in their rooms. Using this power, Ji-su runs a side hustle, secretly peeking into guests’ private lives and leveraging what she learns for blackmail.

One day, she’s assigned to clean the room of a guest who has been haunting her thoughts—Yeon-woo. There, she stumbles upon a memory she was never meant to see.