Otzot. From my deductions, she has the most to gain from fracturing the Cabal. For those unaware, Otzot is the highest ranking Psion within the Cabal. She is the Cabal's lead scientist and treacherous ruler of the Psions. Otzot helped Gaul and co oust Calus due to his desire to free the Psions, which would dilute her status as a freeborn Psion. The fact that Caiatl freed them anyway gives motive to Otzot. As for the "how", it wouldn't be hard to rally other Psions to betray Caiatl. Their race was enslaved for generations, so a recent act of good faith wouldn't quell all the hatred. Using the fractures in the Cabal Empire to finally decimate their prior captors would be a sweet revenge to many Psions. At least that's my deduction