Amanda Susan George is a college student who takes a babysitting job at a remote estate tucked away in the woods, watching over Helen Honor Blackman and Jim George Cole as they head out for an evening. The sprawling house is oddly fortified with many locks on the front door, and Amanda meets the couple’s young child, Tara Tara Collinson, before they tuck in for the night.
After Helen and Jim leave, Amanda makes tea in the kitchen and notices a man watching from outside the window. The doorbell rings, and Amanda is startled to find her boyfriend Chris Dennis Waterman waiting on the doorstep. Chris explains a troubling truth: Helen and Jim are not married, and Helen’s previous husband was placed in a psychiatric institution after an attempt on her life. The two share a tense moment on the couch before Helen calls to check in, and Chris leaves. As he steps outside, a man lurking nearby attacks him, delivering a brutal, repeated beating.
Amanda grows uneasy as knocks echo and she glimpses a silhouetted face at a window. She phones the restaurant where Helen is dining with Jim and Dr. Cordell John Gregson. The restaurant staff alert Helen, who goes to take the call, but the line goes dead. Dr. Cordell later contacts the institution and learns that Brian Ian Bannen has escaped during the night.
At the front door, Amanda discovers Chris, bloodied, beside him stands Brian, who claims to be a neighbor who heard the commotion. Chris loses consciousness, and Brian consoles Amanda while the tension mounts. Inside the house, Brian refuses to let Amanda go upstairs and begins to call her Helen. Realizing that he is Helen’s ex-husband, Amanda inadvertently starts playing into his delusions, professing love for him as a defensive mask.
Brian eventually falls asleep, and Amanda embarks on a perilous attempt to leave with Tara. He blocks her, in the foyer, and the precarious balance of danger and deception continues. Chris regains consciousness and tries to intervene, but Brian murders him. Amanda flees out the front door just as police arrive, only to be hauled back inside when Brian threatens her and Tara with a shard of glass.
Helen and Jim arrive with Dr. Cordell and a contingent of officers, ushering in a tense standoff as they try to coax Brian out. He demands that Helen come inside, yet she negotiates that Amanda and Tara be allowed outside first. Inside, the situation escalates as tear gas canisters come into play. Brian locks Helen inside and begins choking her after noticing the gas canister; Amanda counters by slashing his face with the glass shard and escaping with Tara. The police keep their distance as Helen follows outside and attempts to negotiate, while Brian passes Tara to Helen and advances slowly. With the scene demanding a decisive move, Amanda acts to protect them all and shoots Brian in the head, ending the immediate threat and avenging Chris.
