1988. Beth Soames is 14 years old when her aunt takes her to stay at Raven Hall, a rambling manor. The Averells, the family who lives there, are warm and welcoming, and Beth becomes fast friends with their daughter, Nina. But when they ask her to help them with a harmless game, nothing is ever the same. 2019. Sadie Langton is an actress struggling to make ends meet when she lands a well-paying gig to pretend to be a guest at a weekend party. As day turns to night, Sadie starts to feel that there’s something off about the glamorous guests who arrive at Raven Hall. As the party begins, it becomes chillingly apparent that their unseen host is playing games with everyone...including her.

Seraphine Mayes and her twin brother, Danny, were born in the middle of summer at their family's estate on the Norfolk coast. Within hours of their birth, their mother threw herself from the cliffs, the au pair fled, and the village thrilled with whispers of dark cloaks, changelings, and the aloof couple who drew a young nanny into their inner circle. Now an adult, Seraphine mourns the recent death of her father. While going through his belongings, she uncovers a family photograph that raises dangerous questions. It was taken on the day the twins were born --- and in the photo, their mother, surrounded by her husband and her young son, is smiling serenely and holding just one baby. Who is the child, and what really happened that day?