See moreTrapped in the In-Between, Caly, Mendax, and Aurelius are fighting for their lives - they just don't know whose.
Caly's bond to Mendax from their bonding ceremony and her mortality being tied to Aurelius's from when he saved her life mean the three of them have tangled their life forces together.
And now that they know maintaining both connections is against the natural order of things, one of them must be sacrificed for the other two.