When It Comes to Slaughter is one of Castle's bestselling novels written in the years before he met Beckett at the start of the series. It is one of his 'standalone' books, not part of the Derrick Storm series. Although referenced in the show, it has never been made available in the real world.
(From richardcastle.net) The neo-hippie community of Fair Haven, Vermont, had never experienced a single murder in its nearly 40-year history – until one moonless night a week ago, when five members of the Akin family were brutally hacked to death and found hanging from meat hooks. Suddenly, the town’s tiny two-man police force – Chief Derek Olson and Deputy Ana Ruiz – find themselves thrust into a nightmare world. They wrestle with a dearth of evidence and a populace becoming more paranoid by the second as rumors abound of a scarecrow-like creature with hatchets for hands prowling the countryside. When a second family is butchered in the same gruesome fashion, Olson and Ruiz begin to suspect that many of their townsfolk are not the radical peaceniks they claim to be – the majority, in fact, harbor dark, violent pasts that may finally be coming home to roost.
References in Episodes
Flowers For Your Grave (episode 1.1) – Kyle's apartment
3XK (episode 3.6) - when Castle explains how he researched the Triple Killer for this book.