William P. Ryan, an American journalist, is having lunch with a friend called Anstruther when he hears that the latter is about to visit his sister in Folbridge, Cornwall, at her house called "Treane". Ryan has heard of the place, and tells a story from the recent First World War when he heard of a German attempt to take over a convent during the Rape of Belgium. As soon as the soldiers entered the building it blew up, killing them all. It was proven that the soldiers had no high explosives on them, and speaking with the locals afterwards Ryan was told of one of the nuns having miraculous powers: she brought down a lightning bolt from heaven that destroyed the convent and killed the Germans. All that was left of the building were two walls, one of which had a powder mark in the shape of a giant hound. This scared the local peasants who avoided the area after dark. The nun in question survived and went with other refugees to "Treane" in Cornwall, and Anstruther confirms that his sister did take in some Belgians at the time. In Cornwall, Anstruther finds out from his sister that the nun, Marie Angelique, is still in the area. She has constant hallucinations and is being studied by a local, new, young doctor by the name of Rose, who intends to write a monograph on her condition. Anstruther meets Rose and persuades him to let him meet the young nun.