What to read after The Heart of Shadows?

Luc is a frail child who's afraid of anything and everything, no thanks to his Italian grandmother and her dark bedtime stories. So when he disappears from his bedroom one night, everyone fears the worst. Has he been kidnapped? Did he run away like his sister once did? Little do they know, Luc has traveled to a mysterious land filled with monsters and strange creatures named Shadows and is about to embark on a terrifying journey around the world where he must learn to conquer his fears if he ever hopes to return home. Accompanying him on his journey is the mysterious Uomo Nero, the bogeyman from the nursery rhymes his nana used to sing to him...