Bruen, Ken. Jack Taylor novels.

"Jack Taylor has never quite been able get his life together, but now he has truly hit rock bottom. Still reeling from a violent family tragedy, Taylor is busy drowning his grief in Jameson and uppers when a high-profile officer in the local Garda is murdered. After another Guard is found dead, and then another, Taylor's old colleagues from the force implore him to take on the case. The plot is one big game, and all of the pieces seem to be moving at the behest of one dangerously mysterious team: a trio of young killers with very different styles, but who are united by a common desire to take down Jack Taylor. Their ring leader is Jericho, a psychotic girl from Galway who is grieving the loss of her lover and who will force Jack to confront some personal trauma from his past"--