I've taken a number of liberties with the workings of the Garda Síochána, the Irish police force. To pick the most obvious example, there is no Murder squad in Ireland—in 1997 various units were amalgamated to form the National Bureau of Criminal Investigation, which assists local officers in investigating serious crimes, including murder—but the story seemed to require one. I owe David Walsh special thanks for helping me with a wild variety of questions about police procedure. All inaccuracies are mine and not his.