The House of the Red Slayer is the second in Paul Doherty’s Brother Athelstan series. It is a recent price drop to £0.99 at Kindle UK. And the first title in the series, The Nightingale Gallery, is free right now at Kindle US. So you can try the series inexpensively if you wish.
Doherty is one of the most prolific writers I’m aware of, writing under his own name and variants (PC Doherty), and also under several pen names, including Anna Apostolou, Michael Clynes, CL Grace, and Ann Dukthas. Whew! And, it turns out that a lot of Doherty’s books are pretty inexpensive in both the US and UK: more than a webpage each at $0.99/£0.99 and multiple webpages at $1.99/£1.99. Just go to his author page and sort by price. I’ve read and really liked his Amerotke series, set in ancient Egypt, and also his Alexander the Great series. I’ve also read a fair number of other books of his across many of his other series, although I’ve felt a little more hit-and-miss about some of them.
Anyway, here are links for the specific two I’ve talked about: