The Mystery of Shark Island. The Orinoco voyages, #3

Marooned on a remote outpost in the Greek archipelago, BJ, Graham, Paul and Terry think they are safe from the criminal syndicate they helped to expose in their previous adventure. It is not long, however, before a chance find of a thumb drive throws them into another mystery, and triggers a chain of events that puts their lives in mortal danger. Who is the ever-present Cigarette-Smoking-Man, what data can possibly be on the drive that is so important to desperate men, and who is sending mysterious signals from Shark Island?From a cave supposedly inhabited by a Gorgon, to an old castle that really isn't, and a secret military base under threat, their supposed hideaway soon turns into conflict with a deadly ring of spies.
Swallows and Amazons meets James Bond.