The Hidden Empire  (English, Paperback, Hoornstra Mike)

"Where did you find this bottle with a note from Amonwulf?" Ular asked, wide-eyed. "I found it washed up on the shore while fishing at the ocean," Sofronius said. "It's meaningless, though." "Before you Tempests get all excited," Talura warned, "You should know that these things pop up all over Diaxophas these days. You guys are celebrities. That note was probably written by a kid." "You said that the bottle is meaningless, but you were wrong," Ular said. "This bottle is the key." "The key to what?" Grazio asked. "To Amonwulf being alive," Ular said. When a message in a bottle is found by the Nysterion, the Tempests believe that it is from their friend, Amonwulf, who was believed to have died years ago. Tracing Amonwulf's movements through multiple countries, disguises, prison breaks, lost cities, secret societies, and conspiracies, the Tempests and Nysterion join forces to find out what really happened to their long lost friend.