I was super skeptical starting this book, as I often am with British spy novels. I've seen enough British TV spy dramas to assume the storylines that the UK can throw at me.
I wasn't completely wrong here, as the situation described is a common enough one in the terrorism theme, with its intricate twists and kinds. But this isn't why I continued reading. I kept reading because the characters as written were fresh, detailed and super strange. The strangest is the head of the "Slow Horses" unit of MI5 - this was not someone I'd like to meet in real life. He is slovenly, acerbic & seemingly flaky (the worst of all worlds). It was only Herron's morphing of the character that drew me into the story further.
You can tell what each plot twist will contain before it arrives - there's no true surprise, as it's written like a true pageturner. You expect a certain something to occur, and something entirely different (or opposite) does instead.
There seem to be other books in the series, which I ended up putting on my list in the hopes that the next books will also be fun and character-driven.