The "Seven Traitors" was a group of seven Plumes who stole the mouthpiece of the Pirran Pipe from their piper and travelled to the world aboveground, planning to tell their story and return to lead the Plumes back into the sun.
The Seven Traitors are described as 'goblins'. Small, pale creatures that had been living underground for their entire lifespan. They wore garments that were red as blood. Their faces looked like the faces of dogs.