The Empress of Otherworld

When recently orphaned Hap awakens on his 11th birthday to find that his 104-year-old Great Aunt Benny has forgotten all about his special day, he is hurt. Hurt and angry. So, he decides to explore the one part of her gigantic, rickety, old house that is off limits to him—the Colonel’s Study. In that attic room he sets off a trapdoor that drops him into Otherworld, a fantastic realm made up of many countries, including Oz, Neverland, and Wonderland. In this strange new world Hap must join forces with three super-powered kids—Dorothy Gale, Peter Pan, and Alice Liddell—to overthrow Prospera, the ruthless Empress of Otherworld. As Hap and his new friends battle spider-vultures, trollsons, and the shadowy assassin Peter Panic, he discovers a possible (but dangerous) way home as well as clues to unlocking his very own super-power.
(source: Bol.com)