In 1938, three orphans--Theo, Carl, and Ian, ages ten to thirteen--lead three teachers through a portal that takes them from Dover, England, to Morocco in their quest to locate six silver boxes before the ancient prophecies therein are found by the evil Demogorgon's offspring.

In 1940, when Delphi Keep's taken over by the Royal Navy as a communications outpost, Ian, Theo, and Carl dread being evacuated to the earl's winter residence where they'll no longer be protected, but are even more concerned about deciphering the third prophecy and identifying the Secret Keeper.