Department X was an alleged mortal organization who hunted down and killed mages. Charivari realised that it didn't exist around the time of the War of the Sanctuaries after he was tricked into believing the organisation murdered Warlocks. In A Heart Full of Hatred, it is revealed that a former member of it killed Alice/Winter, Desmond, and Melissa in the alternate timeline, causing Alice/Winter to kill him.
Trivia[]
In Irish Government, ministries of state are known as Departments. This further alludes to the idea that the government was partially connected to the mythical Department X.