Grace Lawson and her brother Donald stand to inherit their late father's millions when they reach the age of twenty-one - but someone in their household of family, servants and regular guests seems intent on ensuring they don't live that long. Donald disappears, and a would-be killer dogs Grace's every move. Not wanting to involve the police and create a family scandal, Grace turns to private investigator Manville Moon - who is unaware of how complex the case will be, or that his own life will be threatened...