Helen Cadel is a live-in maid for PRofessor Warren and his peculiar family in their isolated mansion on the Welsh border. One day, news breaks that there has been a series of murders of young girls and the killer remains at large. When Helen goes for walk that afternoon, she feels herself being watched. And as she reaches the safety of the house, she sees a man lurking in the tree plantation next door - or is it only a trick of the fading light? But when residents of the house begin to 'leave', Helen begins to wonder - could the serial killer be inside the mansion?