The Department of Internal Security was set up by the Mysterious Somebody in January of 1993, following his appointment as head of the PPC the previous year. It was tasked with protecting the integrity of HQ, but under the leadership of the Bracket Fungus, soon became a secret police force with sinister intentions. DIS agents were referred to as "Guards," for obvious reasons.
During the Reorganisation, the DIS fought a civil war with the rest of the PPC that ended with their expulsion from HQ; their headquarters was destroyed, and the Tomb of the Unknown PPC Agent created where it once stood. The former members of this department either left when given the chance and got reassigned, died, or became the Black Cats, and their place in the PPC was taken by three new departments: the Department of Internal Affairs, the Department of External Security, and the Department of Internal Operations. They invaded HQ seven years later, but were mostly wiped out. Any surviving members of the Black Cats/DIS are presumably no longer a threat. According to the PPC Manual, the Board of Department Heads has officially denied the existence of a network of DIS/Mysterious Somebody sympathisers still in HQ.
- Most members of the Black Cats, including:
- Dassie Hyrax (formerly)
- Nyx Nightingale (formerly)
- The unnamed anthropomorphic cat who killed Emily Newton
- Jacob Sullivan (formerly)
- An unnamed orc guarding the Mary Sue Factory
- An unnamed Wookiee guarding the Mary Sue Factory
- The DIS briefly commanded a unit of Daleks in 1999, but these were less agents and more secret weapons