From the Dark oleh Liam V. Devoy

Sean Barrett, Ex-IRA hard man, thought he could live a quiet life in his adopted city, Dubrovnik. When his estranged sister reaches out to Barrett to help save her Marine son Brendan, held by terrorists, Barrett must use his skills and contacts to rescue his nephew, and regain the trust of a sister who blames him for the death of their parents. Barrett enters the world of extremists in the Middle East in pursuit of the terrorists holding his nephew. The trail starts in Libya and leads into the heart of the terror threat As Barrett races to get closer to Brendan, MI6 agent Paul Wilkins trails an elusive "Irishman" based on an intercept from Pakistani intelligence. Barrett meets each challenge with cold efficiency- nothing will stop him from getting to his nephew, but time is running out and who is chasing him?