The Family Upstairs by Lisa Jewell

The novel intertwines the lives of three characters connected by a dark past involving a mysterious house in Chelsea, London. A young woman inherits the house on her 25th birthday, uncovering its sinister history involving a cult-like family and a series of tragic events. As she delves deeper, she discovers unsettling truths about her own origins and the intertwined fates of those who once lived there, leading to a suspenseful unraveling of secrets and the quest for identity and closure.