The Janus Stone

Under the threshold of the old dilapidated house builders found bones of a murdered child. What it was in the hands of sadist? Or ancient, cruel sacrifice ritual?
Detective Harry Nelson, leading the investigation, again appealed for help to the famous archaeologist Ruth Galloway - expert on religious cults of the past.
However, while their only lead - a tale of the rector of the Catholic orphan asylum, located in the house many years ago. Once out of the shelter mysteriously disappeared two children - their tracks and could not find.
Possibly under the threshold of the buried remains of some of these children?
But then who is the murderer?