"Blade of Fortriu" is the second book of what is currently a trilogy.
I found it while doing book processing, looked for the first book
("The Dark Mirror"), and decided to just start reading from the middle
of the series. Marillier is a good writer, so this is possible.
The book is mostly a romance. One of the members of the love triangle
that develops is magical, and the druids and preistesses have some
actual divine powers, which explains why it falls under fantasy, not
romance. The historical events that transpire during the book are
based off of historical fact, and there is a short section in the back
delineating the boundary between truth and fiction. The King Bridei
in the book is based off of a King Bridei who lived in what is now
England in the pre-Christian, post-Roman times.
The non-magical male member of the love triangle is very repressed,
but really good at what he does, which is anything King Bridei asks
him to. I really like his character, and I'm glad the third book in
the series spends more time with him. "Blade of Fortriu" does a good
job of setting up what problems will be tackled in "The Well of
Shades" without having too many loose ends.
Marillier is good with historical romance fantasy books, and this one
is no exception.