As an old house is demolished in a gentrifying section of London, a workman discovers a tiny skeleton, buried for years. For journalist Kate Waters, it’s a story that deserves attention. She cobbles together a piece for her newspaper, but at a loss for answers, she can only pose a question: Who is the Building Site Baby? As Kate investigates, she unearths connections to a crime that rocked the city decades earlier: A newborn baby was stolen from the maternity ward in a local hospital and was never found. Her heartbroken parents were left devastated by the loss. But there is more to the story, and Kate is drawn --- house by house --- into the pasts of the people who once lived in this neighborhood that has given up its greatest mystery.