HarperCollins Publishers Resurrection

When Skulduggery learns of a plot to resurrect a terrifying evil, he persuades Valkyrie to join him for just 24 hours. But they need someone else on their team, someone inconspicuous, someone who can go undercover. Enter Omen Darkly. Student at the new Corrival Academy. Overlooked. Unremarkable in every way 24 hours to save the world. This cannot end well