In the summer between second and third year at Whitehall, Emily accompanies Lady Barb on her rounds of the Cairngorm Mountains, bringing magical help to the locals and searching for new magicians.
For Emily, tired and broken after the events of Study in Slaughter, it should be a chance to relax as well as to visit a new part of the Nameless World, to put her responsibilities aside and just be herself.
But the locals aren't quite what she expects, with problems of their own, and Lady Barb is a different person away from Whitehall. As children start to go missing and evil things are abroad in the night, Emily discovers that a deadly plot is slowly bringing the mountain community to the brink of disaster and that her oldest enemies are about to make a very unwelcome return.