I wouldlike to give less (because I recognize that in this situation the less we give, the more plausible it is for Merlin). But I don't see how we can. Ideally we'd sort the list of all leaks, and discard all the people not in position to affect the outcome of our hunt, all the grunts who wouldn't be told anyway about this before they are called to action, etc. But we just don't have the foci for it. So, I am doing what I think is the next best thing - using subterfuge excellency (our least used favored ability), blaming a divine spirit of betrayal (it's plausible that he might have scrying abilities related to the concept of betrayal), and trying to sell that we have been investigating for a while.Why go this far with it? They're not total incompetents, they just place too much trust in some people.
Sharing something that hints at how we draw power from learning things that are true and secret is a lot less risky than hinting at the crown and avoids a lot of associated complications with pointing fingers.
Even outright sharing that particular ability isn't that much of leak relative to the potential gain here. I don't like sharing things, but intelligence sharing between potential allies sometimes requires steps like this to establish credibility of the data. We wouldn't be giving all the data we have, but as long as what we do give us true and was received from that source it's not really lying to them.
He's a lot more likely to trust that, because it sounds almost plausible. Information spirits like Bob do get direct strength from knowing things beyond what they can be used for after all. Something older and stronger than them that works similarly isn't particularly crazy.
Once the thought is planted he'll likely start actually looking, which should lead him to finding the traitors himself. Even if he doesn't as long as he believes we believe it we get some leeway on our evasiveness.
I am trying very hard to hide the crown while still giving White Council useful intel. The reasons I have for this are:
1) We are both on the side of humanity. That matters
2) Dresden is very much in trouble right now for concealing shitton of stuff he really, really should have reported. This covers for him a bit
3) We are likely to run into political trouble with WC soon, better to butter them up.
How would you suggest I do this? I am open to suggestions.