Pebble in the Sky

One man, Schwartz, suddenly travels from our time to a distant future, where Earth is a minor part of a galactic empire. Because he doesn't understand the language, he undergoes treatment to become a faster learner. A second man, Shekt, is the inventor of said treatment. He is suspected to be part of a rebellion against the empire. A third man, Arvardan, is a visiting archaeologist, trying to prove that human life originated on Earth. Their paths cross, and they are in part connected by a woman, daughter of one, love interest of the other. They need to figure out and stop a plot.