The Rosetta Key

Last seen in Napoleon's Pyramids, fleeing the forces of evil in a runaway hot-air balloon over Egypt, Ethan Gage undergoes further life-threatening adventures in this rollicking sequel.
Nine months before the balloon incident, Gage arrived in the Holy Land with his benefactor, Napoleon Bonaparte. After various misunderstandings involving the secrets of the Great Pyramid, Bonaparte became his implacable enemy. Now, accused of treason by Napoleon's minions, Pierre Najac and Najac's boss, the French-Italian count and sorcerer Alessandro Silano, Gage flees to Jerusalem, where he searches for his former lover, Astiza, who he fears has fallen into Silano's hands. Gage is also hunting clues that may lead him to the fabled Book of Toth, an ancient tome that promises to reveal the secrets of the universe.
Ever the incorrigible gambler and all-around scamp, Gage makes an irresistible anti-hero.