[X] Plan: The Spring and its connections
-[X] Myrmidia (may change to League of Salvation if discussed)
-[X] To kill Mistress Marvos.
-[X] To allow you access to Myrmidia's Spring.
The story goes: Myrmidia orchestrated the play to push us to investigate, and find out about Brother Moulder's smuggling ring that takes the Warpstone extracted from the Spring and sells it to Nagash. Myrmidia wanted to set us on the path to discovering this terrible sacrilege against the divine, a very
specific sacrilege, that risks giving Nagash a powerful connection to the Spring via its material/produce. Such a connection could be used to influence the Spring... or to control it.
Therefore Xenophon says: I need to explore the Spring to see if anything untoward has been already set up. I have the protection of Morr in an investigation that has the blessing of Myrmidia, and I am less important, visible, and connected to sheer magic than the Princeps. If something is already in place, the Princeps going to the Spring might be walking into a trap.
I am uncertain whether we need to use this occasion to access the Spring, but my idea is that accessing it
and doing anything to it is impossible without having the permission to go there.
This plan gives a story, an excuse why
we need to "risk ourselves instead of our precious Princeps", and a moment where we can steal away / kill part of the divinity of Myrmidia. And an accusation against Brother Moulder to take him and his corrupted brotherhood down. Especially because the Princeps will be pissed and possibly a little paranoid that Moulder was "stabbing him in the back in favour of Nagash". What's not to like?
This could even be part of an operation. Ambush the smugglers when they are carrying their product -> the Princeps now has proof and goes to arrest Moulder, we enter the Spring and then go out saying "all is ok".
The only risk is that the Princeps does not believe us at all, follow us into the Spring, and catches us in the act. At which point, Game Over. I wonder if we need to "sell out" the League of Salvation instead of involving Myrmidia to make it more believable. Where "selling out" would mean "there is a league of Batman-people that want to make their own justice of factions that they see as dangerous and corrupt. They organized the play and then gave me hints that helped investigate the smuggling ring". It puts them in the spotlight but not so much as saying "they hate you and want to make a revolution to burn away the corruption and start anew".
Otherwise, if you don't like involving Myrmidia at all, do not care for the access to the spring, and just want to make Xenophon very small and never meet the Princeps again, then I would go Lone Actor + kill Marvos as a cover-up + just ambush the smugglers. A smaller-scale plot and "policing action".