The ides of June - Rosemary Rowe

An
astonishing new order has usurped power in Rome and the reverberations
are reaching even to Glevum, where the legion is preparing to depart. Libertus's wealthy patron, until recently one of the most influential men in the Empire, finds himself not only deprived of the privilege and
protection he had previously enjoyed, but under actual threat both from
the political establishment in Rome and from an anonymous and vindictive
enemy much closer to home.

The murder of another councillor, similarly placed, makes the matter urgent. Libertus, whose humbler status affords obscurity, is charged with spiriting Marcus's young
family away to a place of safety. But his task will bring problems of
its own, as Libertus uncovers a grisly secret and an ancient crime - with ramifications stretching to the present day.