The Seventh SACRAMENT centers around Giorgio Bramante, an archaeologist with an obsession for the subterranean, and one element of it in particular: Mithraic temples which were usually built beneath the earth to begin with. Bramante is an expert - as much as one can be - on the cult of Mithras which was wiped out when the empire adopted Christianity as Rome's sole religion when Constantine won the Battle of the Milvian Bridge.
This is the fifth book in the Costa and Peroni series but can easily be read as a stand-alone novel. I have not t read the first four but one has no problems to follow the story. However I found it a bit of odd that the book starts with two pages explaining the main characters and their occupations. Not a good start and in deed the book- in spite its sensational title - turns out to be a disappointment. The story never takes off, no pace, any real suspense and the plot is pretty disappointing. I found it boring and dragging on and on.
The description of Rome is, however, the main attraction. Hewson does really well in this department bringing the city to life in an admirable way. One feels that he just loves the city. But, this is for me only added value which can not counterbalance the main issue: This is supposed to be a great mystery story and not a travel guide for Rome.
Henson says that he invents from a basis of truth. I wish he would have invented a bit more and in a more gripping way. So all in all, this is a nice try but in the end not to be recommended.