Because Callie can't reveal that she's hearing strange Whispers when she uses her magic, or that she's harboring an Angel's Grace. And if the Sheapheards discover the hellish bargain Roland made, the streets of Rome will flow with blood as brother turn against brother.
And with the Antipope pressuring the Vatican for change, and Nate Temple arriving unannounced to demand an audience with the Shepheards, things couldn't get any more chaotic.
Until Callie learns of an ancient order of traitors hiding in the Vatican, and they'll do anything to bring it down-brick by brick.
The only way to find the traitor, keep her secrets, and save those she loves is to raise her blade against these Holy warriors of God, shattering the Vatican itself.
And the Whispers in her head find all of this so terriblt... amusing.