For two years Lucy and Sam renovated their beautiful Victorian home but spiraling debts are forcing them to sell. The agreement with their real estate agent is that they won't be home for viewings, but when Lucy gets a voicemail saying the Agent is running late, she realizes she will have to show the prospective buyer around herself.

Suffering from extreme anxiety and claustrophobia, Lucy watches the stranger on their doorstep waiting to be let in; she wants to hide and pretend she's not home, but then she thinks of Sam working at all hours to cover their bills, of how much they need this sale, and opens the door.

Lucy takes a breath and begins to show their house. He is well dressed, polite, and despite her unease everything goes well, until he starts acting strangely. Why is he asking increasingly intrusive questions about her and Sam's relationship? Why is he trying to take photographs of her? And why does he disappear into the basement and then not answer her when she calls?

There is something very wrong with this stranger, and now he is refusing to leave...