The Scholar, the Sphinx, and the Shades of Nyx - A. R. Cook - Bog

One reckless decision can change a life.
David Sandoval is a sixteen-year-old genius, more content with studying than being with family or friends. When he is abducted by a gypsy caravan owned by a living Grecian sphinx, he is taken on an adventure through the Curtain, the gateway between our world and the worlds of the "unseen," where many creatures of myth and legend reside.
After discovering that he has unwittingly proposed to the sphinx, David attempts to escape back through the Curtain to the human world, only to be sent to Kyoto, Japan, where he learns a dark secret: a Shade, an extension of the shadowy Night Goddess Nyx, is slowly draining the sphinx of her most precious talents.
David might be the only human on earth with the knowledge to save her, and he must also save his new friends from a ruthless adversary known as the Teumessian.
Can one normal boy truly undo the inflictions of a goddess, and rescue both the seen and unseen worlds from her dark intentions?