Josh Flunk and Spencer Topps are normal schoolboys until, that is, the ivory skull on the old walking stick in Josh's bedroom flashes. Using a secret trapdoor under Josh's bed, they pass through the ancient Egyptian sarcophagus discovered by Josh's Great-great-great-Grandfather to become their alter egos Zac and his assistant Dr Brains, Masters of Zac Zotlan's Detective Agency, and ready to save the world from wearisome werewolves and marauding monsters everywhere. Back in the mists of time, before between the Stone Age and the Iron Age, was the Chocolate Age: an age of prosperity and feasting, but one which came to an abrupt and mysterious end. So when the remains of an ancient chocolate settlement are discovered, extensive work is carried out to unlock its dark secrets. The most precious items unearthed is the chocolate amulet. Although locked securely in a cabinet in the museum, someone manages to take a bite from it, and when they do, the evil CHOCOLATE VAMPIRES, scourge of the chocolate age, are released once more. Time to call Zac Zoltan's Mad Monster Agency!!!.