Ione, on reflection, is feeling concerned about Cheliax's chances of fooling Keltham if Abadar grants more carefully-chosen spells like Abadar's Truthtelling. The Asmodeans may be out of their depth here; possibly she, as a smarter Nethysian, should actually grab that library book and start working out strategies for Cheliax to follow if Abadar grants Keltham a spell like Lesser Planar Ally, or a Conditional Favor that Keltham uses with a condition of 'don't lie to me'.
Well, Asmodeus isn't actually stupid like some of His worshippers, Ione doesn't think. Maybe He'll grant the clerics here appropriate spells like False Future in case Keltham gets Divination, and Undetectable Alignment in case Keltham uses Aura Sight on Ione, and obviously Spell Gauge so they're not caught off-guard by what Keltham receives... though actually, does even the Grand High Priestess have enough caster circles to detect all of Keltham's spells, since it's lowest-first? Ione doesn't actually think so. Maybe they can get Keltham to use the lower-level ones first before they look for the higher ones...
Does Cheliax have a plan B? Is Ione part of it? She's an obvious person that Keltham might try to whisper to, if Keltham notices something wrong. She should ask about that later.