I gave something over 3.5 and rounded up to 4 on here. It was difficult to follow as there were many subgroups and subplots going on, as this was a diaspora of sorts. I found a reviewer who had itemized the characters who traveled together and originated from the same places, thanks going out to her!
I do love Roman Britain and this aftermath is important to understand, the author's note goes into some detail. I would have liked a bit more cohesion of plot, although I assume this was a "scattershot" sort of crisis, and the author gave a good glimpse of what might have been going on.
Coel, who might be "Old King Cole", was a favorite character with some depth.(See Colchester or "Cole's Castle") I also was partial to Llinos and Owain as a couple and their relationship to others had depth.
I would recommend to those who love Roman Britain as I do.