My Horror Movie Synopsis Idea

A young boy named Matthew had always had an imaginary friend. At least, that’s what his parents thought, that Katey was imaginary. When Matthew was growing up, any other person who tried to get close to him would end up harmed or worse, dead. His younger sister was amongst the fatalities which put a rift between Matthews parents, eventually leading to a separation. Initially Matthew was living in the house he’d always lived in, with his Mother until his father tried to get custody claiming his wife was unfit for full time parenting after the loss of their daughter. Katey didn’t like this idea. Matthew wasn’t allowed to leave the house. She traps his parents in the house, tormenting them yet unseen to their eyes. Will either of them get out alive, or will Katey succeed in what she thinks will allow her to have Matthew to herself , forever.