666 AD, south-west Ireland. Sister Fidelma, advocate of the Brehon court, is summoned to a remote abbey. Apparently, two nuns had an unexpected surprise when they raised the water from their well one morning – namely a decapitated naked female corpse with a crucifix in one hand and a pagan death symbol in the other.

Before she even gets there though, the ship that is carrying Fidelma comes across a Gaul trading vessel adrift at sea. There are no signs of a struggle or an evacuation but the ship is abandoned. All that is found is one bloody handprint and a satchel, containing a book that Fidelma had given to her friend Eadulf when she left him in Rome (two books ago) .

Arriving at the abbey, Fidelma finds a deeply antagonistic atmosphere, not just there but also at the fortress of the local chieftain. Everyone has an axe to grind and a finger to point. But can Fidelma get to the truth before more tragedy happens?

The Sister Fidelma series, of which this is the fourth, is rapidly becoming one of my favourite series of historical mysteries. Peter Tremayne has made a clear decision here to write multi-layered mysteries in a historical setting, rather than historical novels that happens to include a mystery. The traditions of the genre are all here – a small cast of characters (with a dramatis personae list), clear relationships – well, clear by the end of the book – between the characters, several non-murderers who nonetheless have dark secrets to hide, and, best of all, calling together all of the suspects at the end to tell them what happened in as roundabout a manner as possible.

Throughout all of this, Tremayne keeps the plot moving forward at all times. I think the best thing I can say about this one is that, despite it being an actual book rather than a Kindle file, I was still carrying it around with me until I finished it. The world that Tremayne has constructed around Fidelma is totally engrossing – Tremayne is an historian, an expert on the era, and the detail is fascinating. Despite it being the seventh century, it is amazing how civilised the world was then.

As for the mystery… pretty good. As I said, there’s a lot of levels here as to who is doing what. If anything, the murder is one of the weaker strands as the motivation seems a little weak, but that might be me putting a twenty-first century mindset onto the characters. Something that seems daft to us probably would not be to the characters involved here.

So, another excellent entry into the series. I think it’s not quite as good as the third, Suffer Little Children, but highly recommended nonetheless. I’m already looking forward to the next in the series. Better say this quietly, but I think Paul Doherty might have competition as my favourite historical author.