Yesterday — Lewis J. Lovhaug

The third book in the "Angel Armor" series! Following the events of "The Cassandra Conflict," Louis Williamson is ready to head back to Earth. In order to find a way back, he must travel to the other continent on Sin in search of a spell to get home. However, the other continent is also Lithmenar's homeland. What secrets does he have about his past that he doesn't want the others to know about