Spook Street by Mick Herron (used)

Twenty years retired, David Cartwright can still spot when the stoats are on his trail. 

The 'old bastard' has raised his grandson with a head full of guts and glory. But far from joining the myths and legends of Spook Street ,River Cartwright is consigned to Jackson Lamb's team of pen-pushing, no- hopers at Slough House. 

So it's Lamb they call to identify the body when Cartwritght's panic button raises the alarm at Service HQ.

And Lamb who will do whatever he thinks is necessary to protect an agent in peril...