The Nonpartment, sometimes refered to as MI18, is an unnofficial division of the British Ministry of Magic.
Founded in 1922 by Rachel Farrow as a cross-departmental office between the Department of Magical Law Enforcement and the Department of Mysteries, the division operates as an interal affairs office tasked with weeding out corruption within the Ministry itself.
The division has no name. Its existence is not formally recognized by the Ministry, while employees and actions associated with it are classified under Unspeakable status. Anyone who claims to work for MI18 is lying, even if they do.