Treat them like their own little ecosystem. Now when the players arrive the ecosystem will adapt, and as long as you have a good feel for it, it will adapt organically, not in predetermined ways. As your players encounter these assassins the clues will write themselves.
I've done the former -- they're working their own angle, and have been adapting to the PCs actions -- but I haven't done a good job of ensuring that the proper clues are being left along the way. Looking back, now I see I had the organization as an ecosystem, but the clues were static. Oops.
NotMe, for your aside.. no, Reading Spectacles should not reveal the cipher. IMHO, breaking a cipher can be as rewarding to a player as beating a BBEG.
Ok, cool. That's what I ruled at the moment ... now I just need to put in a good clue/etc towards the cypher itself!
[MENTION=17085]not_me[/MENTION]
Have you considered using a logic puzzle?
Imagine it is a grid, with clues along the Y axis and possible lair sites along the X access. Say the first clue is a trade route the guild uses leading through a frost giant jarl's territory. Go across your table at place an 'x' under each potential lair to which that clue applies. It doesn't apply to at least one - that's the rule. This allows the PCs to apply process of elimination with each clue they learn.
Very interesting! I like that idea... ... for the next time, sigh, again, I really should have posted this at the start of the campaign. There's only one or two chapters left in this module before they should be at the BBEG's lair. (then it's a break before the final module...)
Thanks all for the insights! I'll probably have to tread closely to the line of 'unsatisfactory paint in the sky with big letters' to wrap this up. And I have retconned things a few times already in the game (usually the next session for just something we clearly moofed up on) so another one or two here might not hurt all that much...
let the clues roll free,
not_me