The Poisoner's Handbook by Deborah Blum
So you'll notice that I tagged this with "instructional" - it's not a how-to manual, per-se, but for those of us with a "how to kill someone and what to do with the body" shelf in their library, this is invaluable.
It's just about as grisly as you'd expect it to be, especially considering every word of it is true. When you stack that up against something like American Psycho (where not even Brett Eason Ellis is sure he's actually torturing those women*,) this proves that truth is often much stranger, much more shudder-inducing than fiction.
This is broken up by year/poison - it starts in 1915 and ends in 1935 - spanning prohibition, alcohols feature heavily in the text. As do things like Arsenic (the "inheritence drug") and Radium (have some Radithor for youthful vitality!) and Carbon Monoxide (still a threat.) Blum is unapologetically on the side of Charles Norris and Alexander Gettler - the team who created modern forensics in America. They were inexhaustible and determined and enthusiastic about their cause. For the entire span of Prohibition, for example, these two - a doctor and a toxicologist - were the most vocal opponents of the Noble Experiment due to the fact that it killed more people than it saved. This crusade is broken up by cases that were investigated by the duo: from industrial poisonings to crimes of passion.
Blum made even the chemical compounds enrapturing and I found myself reading "just one more page" despite the fact that I have a list of things to-do that's as long as my arm. I also found myself thinking that Bones and/or House and/or the new Sherlock on BBC need to do a story arc with a serial poisoner - one who's always poisoning, but changing the poison. It makes me dizzy just to think of it.
A note for those who find themselves squeamish about such things: Blum does not pull punches. If you ever wanted graphic (while remaining extremely clinical) details about what things like Arsenic and Carbon Monoxide do to you, this is your book. Just remember that some things can't be unread. You should get over your squeamishness, though. This book is THAT GOOD.
* I heard that on a Fresh Air interview a million years ago, and I cannot for the life of me find it. Anyone have a source? Or did I hallucinate that?