The Murder Rule, the latest book by Dervla McTiernan, departs from her mystery series starring Detective Cormac Reilly to stand alone. The supposed theme of the book is revenge, but it turns out to be more about misplaced trust.

Hannah Rokeby is a law student at the University of Maine, the self-sufficient daughter of a fragile and damaged single mother. Her father died before she was born, and she has no other relatives who acknowledge her; it’s always been just the two of them, with Hannah knowing from an early age that it will be her job to be the adult in the relationship. Her mother, Laura, has sought all her life to conquer her PTSD using the crutch of alcohol, and Hannah patiently stands by during her ups and downs and encourages her in a daily routine whose predictability helps to combat her volatility and maintain her sobriety.

That all changes during Hannah’s third year in law school. When Hannah was a teenager, she discovered and read Laura’s diary telling the story of the summer of 1994, when Laura found and then lost a boyfriend and was brutalized by his best friend, a man who has since been convicted of the rape and murder of a young mother. When Hannah discovers that a prisoners’ rights group called the Innocence Project at the University of Virginia is seeking to overturn the conviction of the man responsible for damaging her mother so thoroughly, she concocts a scheme to insert herself into the process, posing as an idealist who seeks to help them with their mission so as to undermine it and consign him permanently to prison. But as she maintains her disingenuous façade and digs deeper into the case history, disquieting details come to light that throw everything she knows into question.

I thoroughly enjoyed this book, although there were some implausible bits, legally speaking, that might not happen in an American courtroom (McTiernan was an Irish lawyer for 12 years before turning to writing). Some readers have complained as well about the unlikeable protagonist, Hannah, and in general I prefer a sympathetic character, but in this book her cynicism and duplicitousness work perfectly to set up the story, as well as giving the character added depth. As events unfold, it becomes clear why Hannah is who she is, and enriches the story of her gradual awakening to different possibilities.

I don’t want to give away too many of the plot points here, since a big part of enjoying this book is arriving at them at the same time Hannah does, but the twists and turns as the story unfolds kept me reading enthusiastically from beginning to end. I was initially disappointed to discover that this wasn’t another of her Cormac Reilly series but, having read it, am duly impressed with her ability to write a compelling and entertaining stand-alone mystery/thriller outside of her proven formula.