The Cleaner: Mark Dawson

John Milton is the man the government call when they want a problem to vanish . . . but what happens when he's the one that needs to disappear? After a botched job leaves a bloody trail, government assassin John Milton does the one thing he's never done before: he hides.
Disappearing into London's bustling East End and holing up in a vacant flat, Milton becomes involved with single mother Sharon and her troubled son Elijah, who are caught in an increasingly bloody turf war between two rival gangs.
Unable to ignore the threat, Milton sets about protecting mother and son, meeting violence with violence. But his involvement puts him in the sights of the government's next best killer, and before long Milton is not just fighting to save a family and a home - he's fighting to stay alive . . .
If you like Lee Child's Jack Reacher, Vince Flynn's Mitch Rapp, and Robert Ludlum's Jason Bourne, you won't be able to put down the compulsively addictive John Milton series.