The Stone Demon (The Iron Witch Trilogy)

When the newly-released demons set the Order of the Crow an impossible ultimatum - deliver the Philosopher's Stone, or suffer fatal consequences - alchemist's apprentice Donna Underwood must recreate the mythical artefact before the world is plunged into a modern Dark Age. But will she succeed when she finds herself pitted against a vengeful demon king, not one but two Faerie queens, an immortal Magus with his own shadowy agenda, and her own dangerously unpredictable powers? Donna must be willing to make the ultimate sacrifice, but even death may not be enough.