The Silencer. The Silencer Series, #1

CIA Black Ops agent John Smith is on his latest assignment in London. Little does he know--it'll also be his last. Barely surviving an attack on his life, Smith lays low for six months until he returns to the United States. His flight is strangely diverted to Philadelphia where he meets a mysterious man who knows all about his past and recruits him for a job. Needing a new identity, Smith becomes Michael Recker.
He then tries to prevent bad things happening to innocent people while interacting with several crime factions operating within the city. All the while, Recker plans his revenge on Agent 17 who committed a heinous act that Recker will never forget.