The Janus Stone, Серый

Dr Ruth Galloway's forensic skills are called upon when builders, demolishing an old house in Norwich, uncover the bones of a child - minus the skull - beneath a doorway. Is it some ritual sacrifice or just plain straightforward murder? Ruth links up with DCI Harry Nelson to investigate.
The house was once a children's home. Nelson traces the Catholic priest who used to run the place. He tells him that two children did go missing forty years before - a boy and a girl. They were never found.
When carbon dating proves that the child's bones predate the home and relate to a time when the house was privately owned, Ruth is drawn ever more deeply into the case. But as spring turns into summer it becomes clear that someone is desperate to put her off the scent by frightening her to death...