Lambert’s reference is the Order of Witchers from The Witcher Game series

The Witcher is a 2007 action role-playing game developed by CD Projekt Red for Microsoft Windows and CD Projekt. It was based on the fantasy novel series The Witcher by Polish author Andrzej Sapkowski.

The Witchers in Sapkowski's cycle of the same name are a special category of mercenaries, specializing in the extermination of all sorts of monsters and beasts. In order to increase their fighting abilities, all candidates undergo harsh training and special mutations, which significantly increase their fighting abilities.

The Order of Witchers was an attempt made by kings and affiliated mages in the 10th century to create an order of magic-using knights who would help Nordlings get rid of enemies they hadn't otherwise been able to subjugate, enclose in reservations, or exterminate – monsters. The final outcome of the mutations disappointed most of the mages, who began to call the result "witchers", charlatans capable of nothing more than mere witchery. A few renegades, including Alzur, secretly aided the monarchs interested in continuing the experiment, and the final set of Trials and Mutations was established.

The Order didn't last long, however – its members had abandoned most of the original "knightly" values over time and soon split into a handful of witcher schools, aimed at taking a more professional approach to eradicating monsters.