The Serpent Sons are a cabal of warlocks and necromancers who serve The Serpent. They operate a cell-structure and mimic the hydra-style adage of 'cut off one head and two will replace it.'
The Serpent Sons are not minor dabblers in magic and many have the ability to use Hellfire.
They have made two major incursions in London. The first was the attack on the mundane funeral of the Prime Minister and the supernatural mirror event. (Case File: Black Parade) The second was an aborted attempt to destablise House Pendragon, (Case File: Fall of House Pendragon) thwarted by The Watch.