Still reeling from the dark, traumatic events of her past employment, Millie Calloway takes a new live-in position cooking and cleaning for Douglas Garrick, a wealthy tech mogul in a high-rise penthouse. Douglas enforces a strict, absolute rule: Millie must never knock on or open the guest room door where his wife, Wendy, supposedly rests due to a severe illness. However, Millie begins hearing muffled crying and agonizing thuds coming from behind the locked door, spotting bloodstains on the laundry. Driven by her protective instincts, Millie makes the dangerous choice to unlock the door, plunging herself into a twisted web of domestic deception and sudden violence.