The Clown And The Crab

{AU! Homestuck}
Karkat was kicked out of the kingdom of Alternia because of his blood colour, but really someone in the castle is betraying his troll's at his level of the Hemospectrum. Gamzee and Karkat have a prophecy that they need to fulfill, but since Karkat isn't in Alternia, Gamzee has to go find Karkat.
But who is this troll that's betraying The Grand Highblood?