Dead Lions (Slough House Thriller 2) (Kindle Edition) by Mick Herron 99p @ Amazon

In the Intelligence Service purgatory that is Slough House, where spies mockingly called the slow horses are sent to finish what is left of their careers, their boss Jackson Lamb is on his way Oxford. A former spook has turned up dead on a bus.

Not an obvious target for assassination, Dickie Bow was a talented streetwalker back in the day. Good at following people, bringing home their secrets. Dickie was in Berlin with Jackson Lamb. Now Lamb's got his phone, on it the last secret Dickie ever told, and reason to believe an old-time Moscow-style op is being run in the Intelligence Service's back-yard.

Once a spook, always a spook, and Dickie was one of their own. To unearth Dickie's dying secret Jackson Lamb and his crew of no-hopers is about to go live.