I've loaned the first two of this series to Wendy, so I don't have the books in front of me to refer to, even if I wanted to. This is a mystery series set in 7th century Europe, about an Irish nun and d疝aigh (judge and investigator under Ireland's Brehon law system) Sister Fidelma, and sometimes her friend a Saxon monk Brother Eadulf. The first book, Absolution by Murder takes place at the synod of Whitby in 664 when the rules of the Roman church vs. the Irish church were being debated at the behest of King Oswy to decide which Northumbria was going to follow. As mysteries go, these aren't spectacular, but the period is an interesting one, and the author Peter Tremayne knows quite a bit about it (Peter Tremayne is the pseudonym of Peter [Berresford] Ellis, not to be confused with Brother Cadfael's Ellis Peters, and is a much-credentialed Celtic scholar). I certainly didn't know how much more liberal Ireland, even the church, was with respect to the position of women and the rule of law than, well, practically anywhere in medieval Europe (or even, in some respects, modern Europe).
The second book takes place in Rome, as Fidelma goes to get the rule of her order--St. Brigid's of Kildare--approved and becomes involved in investigating the murder of the Archbishop-designate of Canterbury. Deusdedit, the first Saxon Archbishop of Canterbury died in 664 and in 667 Oswy and Egbert sent Wighard to Rome to be consecrated as his replacement. Wighard died of the plague almost immediately upon arriving in Rome, and Tremayne uses that as the basis of A Shroud For the Archbishop, moving the date back a couple years so that it follows immediately after Fidelma's first case and making Wighard's death a murder for her to investigate. I read these back to back, and I'd say my general impression is that the writing improved a little, but it was still mostly the historical background and only secondarily the characters that held my interest. The mystery aspect barely registered with me at all.
The third, Suffer Little Children, is much grimmer and more about the politics of Ireland, with lots of children and innocent villagers getting put to the sword to further the political ambitions of certain chieftains and petty kings. Again, the details of the roles and responsibilities of the Brehon judges vis-a-vis the kings and the High King at Tara, and the laws and rules of evidence are the interesting bits. As far as characterization goes, Fidelma's friend Eadulf is sorely missed.
I may sound like I have mixed feelings about the series, and objectively I suppose I do, but I rip right through the books and always learn something interesting so overall I really do recommend them--which is just as well, because I've already bought the next three or so and am just taking a short break before reading them. They've actually inspired me to using 7th century Ireland as a backdrop for a D&D campaign, for when I play with people other than my group of regulars (where we have enough campaigns with various GMS under way already).