Two 'Gentlemen' with a very 'evil' reputation amongst the denizens of London Below they are known as Assassins and 'bad business'. They appear to be either very long-lived or capable of time travel, taking credit for the burning of Troy, the delivery of the Black Plague to Flanders, and the torture and murder of a monastery's residents in sixteenth-century Tuscany.
Mr Croup is short and plump, a greasy little man with eyes of faded china blue and a fox-like aspect. He is short of temper with too many teeth and sharp, piggy little eyes. He is extremely verbose, padding every sentence with unneeded complexity. Mr Croup appears to have the knack of shifting through time and space and can use this ability to teleport short distances with a fading flash of shadow.
By contrast to Mr Croup, Mr Vandemar is very tall and with brown eyes that make him look more than a little wolfish. Possessed of a lower cunning than Mr Croup, Mr Vandemar appears enormously strong and extremely tough. Mr Vandemar is rather simple and straightforward in his approach, much less sophisticated than Mr Croup, monosyballic and very literal. He speaks with a Scots accent. Mr Vandermar possesses superhuman strength, an enhanced sense of smell, the ability to regenerate most wounds, highly adhesive saliva, and the ability to eat anything that will fit in his mouth.