The Incendium Maleficarum has been lost and Carter Weston presumed dead, but the story of That Which Should Not Be is only just beginning. Now Carter's only daughter, Rachel Jones, and his oldest friend, Henry Armitage, must embark on an epic journey that will take them from the hell-blasted Tunguska forest to the catacombs of Paris to the shores of the Scottish Isles. They are in a race against time, for in France, strange murders and whispers of occult rituals herald the rise of an ancient evil bent on plunging the world into eternal darkness. It is up to Rachel and Henry to learn Carter's fate, recover the Incendium Maleficarum, and perhaps even save the world.