First published in Great Britain by HarperCollins Children's Books in 2017

"Valkyrie Cain has been out of action for years, recovering from the war against her alter-ego Darquesse, which nearly destroyed her and everyone else. Some things never change though: bad people still want to do bad things, and Skulduggery Pleasant is still there to stop them. 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"--Amazon