It has been five years since the disappearance of Katie and Hunter, and a suburban family witnesses strange events in their neighborhood when a woman and a mysterious child move in.
Alex (Kathryn Newton) films her younger brother Wyatt’s soccer match. At Alex’s house, she shows her boyfriend Ben (Matt Shively) the treehouse in the garden. Here they discover Robbie, the neighbor’s child. Puzzled with why he is here, she takes him back to his own house across the road. In the early hours of the next morning, Alex hears an ambulance outside at Robbie’s house. The next day Robbie turns up at the house after Alex’s mom Holly (Alexondra Lee) offered to look after him for a few days because his mother went into the hospital.
Later on in the day Alex finds Wyatt and Robbie in her treehouse talking to Robbie’s invisible friend. In the evening Wyatt is playing multi-player on the Kinect by himself with Robbie sitting on the sofa.
Ben asks who Wyatt is playing with and Robbie tells him it’s his friend. When Alex arrives in the lounge Ben turns the lights off in the lounge and shows Wyatt through the camera the infra-red tracking dots. As Alex, Ben and Wyatt dance in the dark and Robbie sits on the sofa, the camera picks up something moving on the sofa next to him.
Stranger things unfold in the following days leading to more horrifying experiences in Alex