A good overview of the science, such as it is, and a surprising number of practical notes from the author. (tl;dr: There is no definitive way to detect liars. All of the pop-sci body language stuff is rubbish. Go with your gut, and check everything checkable in the subject's statement. Polygraphs are only useful for scaring people into confessing, which doesn't work when they know what a polygraph is and how it works.)