This is definitely one of those "so bad it's good" books, but unfortunately, it's neither bad nor good enough. Not enough sex (or torture) to be really sleazy. It takes itself way too seriously with all the patriotism and Union Jack-waving shit. And, most importantly, there's zero (intentional) humour in this one. So it is hardly surprising that it remains the sole entry of the eventual Mrs Storm Frend series even though it closes with the usual "knowing that one day he would summon her and that she would go back".
Which is too bad, really. I would definitely check out its sequel. Badass heroines always have potential, and a follow-up could shine with a more coherent plot and some editorial effort.