Fourteen-year-old Valkyrie and the skeleton mage, Skulduggery Pleasant, try to foil a plot set in motion fifty years before to find and open the gate that will allow the Faceless Ones to return to this reality.

War is coming. To avert catastrophe, Skulduggery and Valkyrie are sent on a secret mission that takes them away from everything they know, to a forsaken land of magic and grim, unrelenting terror. It is here that Valkyrie will have to fight the hardest - not only against the enemies who want her dead, but also against her own self-destructive impulses. It's only by crawling through darkness that she'll be able to once again stand in the light......

While Valkyrie is off trying to recover her sister's lost soul, it is up to Omen Darkly to be the hero and save thousands of innocent people.

Following the loss of Valkyrie Cain, Skulduggery Pleasant must track down Darquesse before she turns the world into a charred, lifeless cinder -- and so he draws together a team of soldiers, monster hunters, criminals... and Valkyrie's own murderous reflection. Not everyone gets out of this alive.