Lyon Sprague de Camp "Thalia - Gefangene Des Olymp"

XXVII-th century Earth is united by a worldwide democratic government presided over by a constitutional monarch, though the former is veering toward totalitarianism and the latter is a megalomaniac. To neutralize the World Emperor the power-hungry prime minister has ceded to him control of Greece for use in a mysterious secret project. Now Greece is surrounded by a force field cutting it off from the rest of the world, and people of Greek descent everywhere have vanished, presumably spirited away to the isolated region by the Emperor's agents…