"Twelve Days (John Milton #14)" by Mark Dawson

John Milton is a recovering alcoholic, ex government hit man who is unable to find his place in the world or peace within himself. He returns to England to check on past friendships and becomes embroiled in the world of boxing. The tension moves higher and higher as he tries to do what is right and after some stumbles, he is able to accomplish this. 
It is a good story, although  it is prone to having too many cliche descriptions. It all turns out well in the end and he even gets a good Christmas dinner.