Faerie Lord (The Faerie Wars Chronicles #4) by Herbie Brennan

Henry has all but forgotten the Faerie Realm since he returned to his normal life two years ago, but now his past has followed him home. Out of nowhere, Henry's old friend Pyrgus appears-looking like a middle-aged man-and his life is turned upside down once more. Determined to help his friends, Henry returns to the Realm, hoping to find a cure, and perhaps win his way back into the heart of Queen Holly Blue. But what Henry, Pyrgus, and Blue don't know is that the plague is hardly an ordinary disease...

Dog Gone note: This book is in excellent condition.