When Rob and Millie's father goes missing in action while serving at the front during the First World War, the children desperately search the hospital trains returning to Edinburgh with the wounded. But there's no sign of him. While hiding their puppy in the nearby woods in order to stop him being sent to the front, Rob and Millie come across a building full of doctors treating soldiers with shellshock and other nervous disorders - but overhear a conversation that suggests this could be a mask for altogether more nefarious activity. What is really going on at the hospital? Who is the ghostly figure the children spy looking out of one of the top windows? And will their beloved father ever return to them alive?.