This is a start of a series and — unlike some series of thrillers or mysteries — each book is better than the one before. But you need to start with the first one, which is Slow Horses. "Slow horses" are disgraced MI5 agents, British intelligence agents — people who did something a little stupid but have too many connections to be fired. What River Cartwright did is badly screw up a surveillance assignment. (He's convinced he was set up by his rival.)

Now, the slow horses have a new task: A kidnapping and a potential beheading has been announced in London and it's up to the slow horses to try to figure out what's going on.

I love the characters in this. The guy who is the head of the slow horses is this man who is the most thoroughly disagreeable person that many people will ever read about. I read an interview with Mick Herron where he said he just thought of the worst thing that anybody could say in every situation — and that's what River's boss said. It's just great fun.