The White Devil of Dublin. Ryan O'Clery Mysteries, #2

When Detective Ryan O'Clery receives a phone call from a noted historian claiming to have information about his family, he is certain she is mistaken but agrees to meet with her. When he arrives, however, he finds she's been murdered and her computer stolen. His investigation will take him back to 12th century Ireland, a time of the Viking invasion and conquest, to a man known as The White Devil of Dublin, and to a secret his family kept hidden for over eight hundred years.
It will also bring him face to face with an arch enemy determined to finish the job he started. The White Devil of Dublin is the sequel to The Tempest Murders, a 2013 USA Best Book Awards Finalist and 2014 International Book Awards Nominee, though it can be read as a stand-alone.