VOW OF BLOOD by Debby Feo

What was it like to be a vampire in Rome in 84 A.D.? Gaius Domitius Tubero knew well. The life he was forced to live was not a happy one. Scorned by most, he was lucky to have even survived being forced into the dangerous streets of Roma, at a very young age. To stay alive, Gaius had to drink blood. Blood was easy to find, in and around the Coliseum, during the reigns of Caligula and Nero.

Sometimes it was the blood of an enemy. Sometimes it was that of a friend. And sometimes both.

It's been said that one should keep one's friends close, and enemies closer. The problem in the Rome of Caligula and Nero was to determine which was which. In the process of finding out, Gaius learns that while he might be immortal, he was not invulnerable. And the stakes were too high to risk making a mistake.