This is a substantive (478 pg) volume that details a US interrogator's time in Afghanistan shortly after the US-led invasion. I found it quite interesting - it follows the author through his training in US military facilities through his subsequent career in US military intelligence and into his deployment to Afghanistan.
One of the real take-away points I got from this was just how strongly and effectively an interrogator can apply pressure to a suspect without breaching the Geneva Conventions.
This is not a 'how to..' book on interrogation, nor is it a detailed observers account of interrogation as an entity, the history of interrogation or US units it is one man's account of his own experiences from his perspective over his career.
However it is intended to be very educational, this guy is no Andy McNab, he presents a full explanation of a number of 'case studies' that he personally handled in an operational context and outlines the tactics and procedures that US military intelligence uses.
PS - there's no waterboarding before you ask.