The Ruin by Dervla McTiernan

When the police tell Jack Blake's girlfriend, Aisling, that he committed suicide, she has a hard time believing that Jack would take his own life. His older sister, Maude, who left Ireland twenty years ago, is even more convinced that Jake was murdered. Detective Cormac Reilly, who first encountered the siblings when their mother, Hilaria, died of a drug overdose, now works old cases and is asked to take another look at Hilaria's death. As a newcomer from Dublin, he is finding the office politics of the Galway police station puzzling and feels that someone is trying to keep him off-track with his investigation. Could the deaths of Jack and Hilaria be connected, and is either one of them a murder? In this first book of the Cormac Reilly series, McTiernan writes a mystery with characters that the reader finds interesting and cares about. Reviews have said that the author is similar to Tana French, which is an apt comparison.