Operation Typhoon Shore (The Guild of Specialists, No.2) by Joshua Mowll
After being lashed by a typhoon on their uncle's ship, THE EXPEDIENT, intrepid siblings Becca and Doug MacKenzie want nothing more than to escape from the volcanic island on which they're stranded and resume the search for their parents. But their uncle, Captain MacKenzie, seems more concerned with the missing gyrolabe than their missing mother and father, and he refuses to discuss the role the mysterious Guild of Specialists played in their disappearance. As the formidable Kalaxx warriors close in on their hidden cove, Becca and Doug unearth a riddle linked to a 1533 painting, which may hold the key to the Guild's dark secrets and to finding their parents. But how can they possibly solve the puzzle and escape with their lives — before their enemies attack?