"...understood. Good luck, Keltham."

Off he goes.

Keltham needs to talk to the highest-circle cleric of Iomedae that can potentially be obtained on short notice, possibly including by somebody Greater Teleporting to Lastwall or Mendev or wherever to get them.

There's a small delegation here specifically to talk to him, but if he wants the highest-circle cleric that's...probably Queen Galfrey of Mendev. Who is probably going to be somewhat reluctant to come to Osirion, can this be done over a scry or anything?

...'Queen Galfrey' sounds like she might be an overly predictable info-target, if she's literally the highest-circle cleric.

How about if Keltham describes the basic situation to one Osirian in a position of authority who's pretty unlikely to be kidnapped for that information, and then they decide how to put him in touch with a slightly less predictable high-circle cleric of Iomedae, very quickly?

Sure.

Great.  Even if Abadar's bargain with Asmodeus still prevents Cheliax from kidnapping or Maledicting Keltham, which is, possibly, something else that should be asked about if it hasn't been asked already, there might be other world actors with an interest in not having Keltham destroy circles carved out of Cheliax.

Keltham needs to do his best to dump his guess about how to destroy circular sections of country, into an Iomedan cleric sworn not to use that info without permission from Keltham.  Unless Keltham is taken off the gameboard, by non-Iomedan forces, in which case Iomedae's adherents are free to do whatever they want with that info and are specifically encouraged to use it to destroy Cheliax if Cheliax makes trouble.

It should not be easy for adversaries to guess which cleric of Iomedae has this info.

- the cleric of Abadar nods seriously, looks absolutely miserable, and says he can get a somewhat arbitrarily selected sixth circle cleric of Iomedae here in ten minutes, and that that's the kind of agreement a cleric of Iomedae would keep.

...can Keltham divide the knowledge into two portions, such that it's only dangerous when two oathsworn clerics combine the pieces?

It doesn't seem like the sort of thing you could reasonably do with the knowledge underlying - no, wait, he's being dumb.

"Please get me a book, any book, that wouldn't look at all out of place or unusual in that Iomedan cleric's home library, preferably without anybody else observing which book you took.  And having the cleric here in half an hour, instead of ten minutes, is fine, because I need to write things down anyways.  With very strong guarantees about nobody watching me write."

Here's a leather-bound book about the First Crusade.

"For an absolute assurance no one is watch you or could get authorization to do so I will need to put a request to the pharaoh. I'll do that now."

He will swear that no one is permitted to read over Keltham's shoulder, that He thinks He'd know if anyone could, and that scrying within the Dome is supposed to be impossible, plus they'll have Mage's Private Sanctum up which is also categorically sufficient against non-gods.

He'll write down, one-time-pad encrypted and in Baseline, four guesses for Wish phrasings that will conjure antimatter, along with some half-assed calculations about how to adjust the numerical parameters to destroy different sizes of map circle, plus a lot of explanation about what the phrasings mean, the underlying equations implying the existence of antimatter and how to anchor the meaning of those terms in observable reality.  Once decrypted, you're going to want a wizard to understand that math, and you might be further helped by checking in with Ione Sala if nobody else around understands concepts like electrical charge and quantum spin already.

If that doesn't work, try squeezing a lot of hydrogen together, or conjuring it in tight proximity to itself.  Here's three guesses at a Wish phrasing that'll do that...

If that doesn't work, try conjuring a relativistic projectile, careful where it's aimed at, but pointing it towards the center of mass for Golarion seems like it should unambiguously point 'down'...

...Wish phrasing that steers an asteroid into Cheliax, where Keltham has tried to phrase the Wish to put upper bounds on the mass and the impact velocity, but it's not impossible that something like this is what went wrong with the Starstone impact, and Wishes do have a reputation for going wrong, so maybe consider this one something of a very last resort.  Probably still better than Cheliax taking over Golarion and becoming a factory for souls going to Hell, though.

And sixth-circle cleric Koenraad Breker, of Lastwall, is urgently teleported to Osirion with a briefing that consists of 'the outsider who started the godwar wants you to talk with him about superweapons'. 

He has not in fact been told, at all, about the outsider who started the godwar, but that's all right, he can take things in stride.

Hi.  Welcome to Keltham's life.  It is, by Golarion standards, a complicated one.

Yada yada extremely serious oaths please yo.

He will read over Keltham's requested oath wording, contemplate it thoughtfully, ask if the text of the oath is itself to be a secret, pray on it for a few minutes...

....and swear to it.

Right.  If you combine this book and this sheet of paper, using a code that does not get written down, but should be simple enough to memorize, you get ten different guesses by Keltham at a Wish phrasing that could destroy Cheliax, or more generally, an arbitrary circle drawn on a map.  They have adjustable parameters depending on how large a crater you want to create.

The sensible thing to do here, and what Cheliax should expect Keltham to do if they're modeling him almost correctly, would be to pull in a high-circle wizard trusted of Iomedae, who knew what there was to be known about Wish phrasings, and have them work with Keltham on adjusting these.

Keltham cannot do this because he is in the middle of a complicated situation that he has not in fact decrypted, he has suspicions he's trying to not think about too hard, and he was told in a vision from Iomedae that Cayden Cailean might possibly have had good reasons for destroying Iomedae's intelligence apparatus in Cheliax which implies that they might be dealing with information hazardous to Iomedae Herself.

Keltham's current plan is that he's going to have to find out what's usually known about Wish phrasings on his own without any help from Iomedan or Abadaran forces.  Afterwards he may hand over an improved set of Wish phrasings for destroying things.  Until then, they're going to need to take the information here and work out on their own how to adjust the phrasing, if it comes to that.  All this is to be understood as an emergency measure intended to prevent Cheliax from definitely winning immediately if somebody takes out Keltham permanently, and to make that Chelish victory be not a thing that is knowable to somebody predicting Keltham.

...understood. Wish phrasings he came up with himself almost definitely won't work but it does seem like they're a better starting point than nothing at all, and as an emergency measure they'll pull in everyone they can to improve on them.

If Keltham is taken out and the info here is not understandable without context despite Keltham's best efforts, as would not be terribly surprising, they can hopefully ask Ione Sala, the Oracle of Nethys, currently findable in the Temple of the All-Seeing Eye.  Ione is forbidden to help Keltham about anything that matters, but she may be able to help Iomedans.

If Ione Sala isn't allowed to help with this - unfortunately Keltham did not think of this fast enough to ask her - spend whatever resources are required to rescue Asmodia of Project Lawful from Cheliax.  Carissa Sevar also has this knowledge, but will not willingly help destroy Cheliax, so only go for her instead if Asmodia is unreachable and you think you have sufficiently good mind control.

"Or something sufficiently transformative short of destroying Cheliax - does she care who rules it?"

"I straight-up do not know exactly what is up with Carissa.  Ione might know better."

"Do you want me to try to make sense of the information, in case that gives you ideas for what else to include here so that we can better reconstruct it? We could use Modify Memory or similar, afterwards, if you want to avoid the information being known by me."

"Sounds like a doomed endeavor!  Sure, let's try that.  Couple of other notes first -"

In the event that Keltham gets removed from the gameboard, they should possibly consider trying to spring an ambush on Asmodeus, Urgathoa, or whichever other god is being most inconvenient to Iomedae's plans, by Wishing for some very dangerous material in vacuum containment that will automatically fail if magic is removed from it; which you could maybe drop onto the ninth layer of Hell, and create an explosion large enough to destroy whatever chunk of Asmodeus usually lives there.  Less than a minute before they destroy Cheliax, would be the plan there, ideally; you can lose the advantage of surprise to a god in a few rounds, if you destroy Cheliax first, but an assault on Asmodeus shouldn't alert Cheliax as quickly.

Is Iomedae by any chance bound by known agreements, concessions, which would prevent Her from directly participating in a plan like that?  Maybe even require Her to shut down a plan like that, if She learned of it?

Keltham also needs to write a testament giving over his Project Lawful shares to somebody not in Cheliax, if Keltham permadies.  The pharaoh of Osirion is an obvious choice but Keltham is open to hearing how an Iomedan would be a better choice.  Keltham is pretty sure that he is more aligned with Iomedae than Abadar; he's nowhere near as sure about the Pharaoh of Osirion versus the Queen of Mendev.

Keltham could give the funds in trust to the pharaoh of Osirion and ask that they be spent according to Keltham's values, less a stewardship fee; that's the kind of thing Abadarans are good for. If it goes to Queen Galfrey it'll probably largely be spent funding a crusade, which is a good use of it but if there are new opportunities opened up by weird shenanigans she won't be particularly positioned to identify those except insofar as they're relevant to fighting the Worldwound.

You can only drop something on the ninth level of Hell from the eighth level of Hell; in this manner Asmodeus ensures He is very hard to take by surprise. 

"....We have to destroy Hell, that is the highest priority for Good and for humanity. I cannot imagine Iomedae would have willingly agreed to promise not to destroy Hell, and I know that hypotheticals have been entertained under which we'd do it. I don't know most of the god-agreements that exist, and it's quite possible she's agreed not to do it under some particular sets of circumstances, but...what would be the point of a god of destroying Hell who isn't allowed to do it? ...more likely, there could be something Asmodeus is allowed to do if Iomedae does or enables that, which She thinks is sufficiently bad that it's worth Her not helping with the plan in order to avoid Asmodeus being permitted the retaliation."

"I'll count that as a weak strike against my inchoate theories of what was actually going on with Iomedae and Nethys and Cayden Cailean, which I guess is not too surprising at this stage.  Hell is the priority, not Abaddon or the Abyss or, obviously, Pharasma?"