"An Emperor for the Legion" is the second of four volumes in the Videssos Cycle. At the end of "The Misplaced Legion", the Emperor had been killed by the Sorcerer of Yezda and the Videssan army had been routed due to the failure of Ortaias Sphrantzes to hold his section of the line. The army has been split into several parts, each with no contact with the others. Ortaias has one part, the Thorisin Gavras has another. Gavras is viewed by many as the rightful heir to Videssos. The rest of the army is under the command of Marcus Scaurus, the misplaced Roman Legionary. The plot of the first book in the series took a Roman Legion and through an accident of magic transported the legion to another world. They hired on with the Empire of Videssos as a mercenary company and with the murder of the emperor, Marcus is seeking the one man he is willing to follow: Thorisin Gavras.
Much of "An Emperor for the Legion" is one long march. Marcus and his Romans, plus the rest of the army, is on the march through lands controlled by the Yezda and have to deal with random attacks. After finally meeting up with Thorisin, they return to the capital city of Videssos only to find it occupied by Ortaias, claiming to be the new Emperor. Marcus and Thorisin need to decide if they can accept the rule of Ortaias, or if attempting to assault the nearly impenetrable fortress city is worth the cost.
This book is the logical extension of the story after "The Misplaced Legion". We do not see much character development of the Romans (or anyone else), but by spending more time with the Romans we get a better sense of who the men are. Call it "character explanation". The initial intrigue of sticking a Roman legion in a completely alien world in which magic is fairly commonplace has worn off by this point, but Turtledove is able to tell an interesting story with these characters. After this novel, the focus seems to be on the politics of Videssos seen through the filter of the Roman Legion. It's good, and very detail orientated. "An Emperor for the Legion" is a slower moving tale, but the series is an interesting one.