The Union's instrument of internal security, tasked with rooting out treachery and extracting confessions from those suspected of it. The Inquisition operates under the authority of the Arch Lector and employs Practical methods - torture, imprisonment, and the systematic destruction of suspects - justified by the necessity of protecting the state. Superior Sand dan Glokta is its most effective practitioner and its most self-aware one: he applies his methods with professional precision while remaining entirely clear-eyed about what he is doing and what it has cost him. The Inquisition is one of Abercrombie's central satirical targets - an institution that perpetuates itself through the fear it generates and the confessions it produces, regardless of their truth.

The Inquisition's hands-on operatives - the people who carry out the physical work that Superior Glokta directs. Practicals wear hoods and do not speak during interrogations, a convention that preserves their anonymity and the Inquisition's mystique. Severard and Frost are Glokta's regular Practicals in the trilogy, each characterised by a specific kind of competence. The Practicals are one of Abercrombie's wry observations about institutional violence: the people who do the actual work are anonymous, loyal, and entirely without the philosophical framework their superior applies to the same actions.