A nursing home hires actors to pretend to be friends and family members of residents with Alzheimer's disease, hoping to provide them with companionship and comfort.
Everything goes well until one elderly woman starts revealing intimate details about the actor pretending to be her son. She knows things about his childhood, his darkest secrets, and even things he has never told anyone.
Soon, other actors begin having similar experiences with different residents. Some patients speak in the voices of the actors' deceased relatives. Others know things they couldn't possibly know.
Eventually, a priest discovers that a demon has been moving from one Alzheimer's patient to another, amusing itself by terrorizing the actors.
The demon finds the whole situation hilarious. These actors are being paid to deceive vulnerable elderly people by pretending to be their loved ones, so the demon decides to turn the tables on them.
The nursing home becomes a terrifying game of hide-and-seek. Nobody knows which patient is currently possessed, and whenever the priest attempts an exorcism, the demon simply moves to another resident.
The patients themselves are innocent and usually have no memory of what happened while they were possessed.
Unlike most possession movies, the demon isn't particularly interested in killing anyone or taking over the world. It just enjoys playing cruel psychological games with people.