The 'Men in Grey', formally known as the Department of Domestic Defence, appear to be a human organisation devoted to keeping the supernatural secret. Though they had apparently been around for centuries, the home secretary Alistair Frith shut them down, eventually driving Mr. Rook to come under the control of Captain Hatch.
They were next seen threatening a young girl who had witnessed Tom as a werewolf, ensuring that she would remain quiet.
They claim to have been around for as long as werewolves, vampires, and ghosts.
Although they appear human with no supernatural powers, Mr. Rook could at least partially detect the presence of Alex in the room.
A clipboard containing a list of events they covered up had columns to check off for which type of supernatural was involved in the event. These columns include Type 1 (ghost), Type 2 and Type 3 (vampire and werewolf), Type 4 (zombie), Type 5 (incubus and succubus) and an unknown Type 0, possibly referring to humanity. They have a different classification system as the CenSSA, which describes vampires as Type 1 and ghosts as Type 2.
Throughout the fifth series, a major storyline is Mr Rook's efforts to secure funding for the department, as their government supervisors believe that the funding needed by the organisation is excessive and the threat posed by the supernatural has been exaggerated. After making contact with Hal, Tom and Alex, Mr Rook attempts to use them to provoke a rampage that would prove the necessity of the organisation, but the trinity were always able to defuse the situations (And Rook was partly manipulated by 'Captain Hatch', who sought to trigger a vampire/werewolf conflict that would restore his power).
Rook's efforts seemed to come a conclusion when Hatch, his power restored to a manageable degree, appeared on live television and nearly drove the population of Britain to suicide with his 'spell'. Rook was able to kill Hatch's body, with the threat he posed and the death left in his wake proving sufficient to reignite interest in funding Rook's department, although Rook himself was asked to resign. This, however, was shown to be an illusion created by Hatch and Rook's actual fate is unknown.
List of appearances
- The War Child (Last episode of series 4)