The North Hollow files were a collection of sensitive information on various members of the Star Kingdom of Manticore's political high society. The Earls of North Hollow used these files to blackmail other people in their interest.
The files included information concerning Baron High Ridge's involvement with the Jordan Cartel, as well as a detailed account of the actions of the cabal that planned the assassination of King Roger III. (HH4, HHA2.3: QG)
Georgia Sakristos worked as the keeper of the files, and was the one who finally destroyed them (by blowing up the North Hollow mansion) after she was herself blackmailed by Anton Zilwicki and Catherine Montaigne. Zilwicki speculated that as much as a third of the information in the files was false or faked. (HH10)