Dark Days - Derek Landy, HarperCollins Publishers

He’s dead. She’s deadly. The bad guys don’t stand a chance. The fourth book in the bestselling Skulduggery Pleasant series. Skulduggery is gone, sucked into a parallel dimension. There is no OFFICIAL plan to save him. But Valkyrie’s never had much time for plans. ‘A thoroughly satisfying blend of humour, magic and adventure’ Rick Riordan, author of the Percy Jackson series