The Black Stone
This is the fourth in Nick Brown’s Agent of Rome series, following the adventures of Cassius Corbulo and his faithful sidekicks Indavara and Simo. For those unfamiliar with the series, Cassius is a Roman centurion in the 3rd century AD, but he is not in the regular line of command, being more what we would call an Intelligence Officer. He joined the army hoping for an administrative post and claims to hate violence, but as he admits he has been consistently unlucky. The Black Stone is as violent an adventure as its predecessors, although Cassius himself handles a weapon only once.
Like the other books in the series the story is set in the eastern reaches of the Empire, and it centres around the emergence of a religious cult in the Arabian desert which challenges the authority of Rome. The cultists seize a black rock which is considered sacred, and it is Cassius’ mission to infiltrate the enemy camp and retrieve it.
The Black Stone is quite a lot longer than the earlier books, and the author seems to want to plough a deeper furrow. There is more about the relationships between the protagonists and in particular about their religious and ethical beliefs (Simo is a Christian). I am not sure that all followers of the series would welcome this, but they need not fear that the action has flagged. There are plenty of swordfights and action of all sorts, and if you liked the earlier books you will enjoy this.