Good historical thriller, which fitted in well to what I believe I know about 17th Century 'British Isles'. The plot had many stock historical themes from the Civil War and Protectorate periods. That isn't a criticism, as historical fiction without strong anchors in well studied events is very difficult to buy into.
The book is well enough written, conveying all the hardships and customary behaviours associated with those torturous times without every straying far into harsh graphic detail. This creates a book for a very wide readership. We are given the colours and outlines, being left free to paint the stronger images for ourselves. That doesn't mean the story lacks bite, far from it.
The characters are drawn with a depth of individual and understandable emotions and prejudices, especially in the light of the historic backdrop. As one living much of my life in one of the last country houses to hold to the King, in one of the strongest Royalist areas in the Civil War, I have always had an interest in that history. I read nothing that grated against my preconceptions. I wish I had written this plot.
Of interest to me is the strong connection this book has with so much that is currently happening as a result of interactions between prejudiced religious beliefs and cultural intolerances. I don't know if any of this was in Allen's mind as he wrote, but it was certainly in the mind of this reader.
To summarise: a good plot, with familiar historic anchors from an exciting period, written well.