[3.5] How to have a fun solve-the-mystery session

[Snarfmite]

In my game's next session, I want the PCs to investigate some magic shops and try to figure out if any shopkeepers are aligned with one of the Thieves' guilds in the town.

I'd like suggestions for interesting backgrounds for the shopkeepers (Thieves or not) and for ways that the PCs could know for sure whether or not they are Thief-aligned. Those shops that are thief-aligned will have a letter containing important information and confirming the shopkeeper as loyal to the thief's guild. However, the PCs might not find it, and I want other ways to confirm their suspicions. I'd love to be able to leave clues for the PCs to find and put together, but I have no idea what the best way to go about doing that would be, without giving everything away after the first clue.

Also, how should the shopkeepers react to queries? If any of the thief-aligned shopkeepers knows the PCs are actively looking for them, they will hire an assassin or two to hunt down the PCs and alert other members of the thieves guild.

I think the PCs might try to break into the shops at night to look for information, so what sort of anti-theft defenses would be in place for a medium-large sized magic shop in the capital city of an empire?

Can anyone see any other good options for the PCs? One or two of them could pretend to be Thieves guild members and tell the shopkeepers they have important things to discuss with them. Or they could come right out and tell the shopkeepers they are looking for information regarding thieves guild activities and see how the shopkeepers react. Finally, they could try an elixir of truth, but I don't think they'll be smart enough to do that.

Has anyone run a similar session before? How did it turn out? I want to make it exciting and memorable, but I want to make sure it's not too complex to be fun.

[fryplink]

Make it so that Thieves guild operated shops have a token, and its always the same, so that in about half of the shops this single object (Not for sale) keep showing up!

[Snarfmite]

Make it so that Thieves guild operated shops have a token, and its always the same, so that in about half of the shops this single object (Not for sale) keep showing up!

Excellent idea. I was considering a physical tattoo/mark on the shopkeepers, but that would have been too obvious.

[bokodasu]

Cribbed from an Agatha Christie novel, of all places: have a code phrase like "do you have any tanglefoot bags?" Normal shopkeepers will produce them, naughty shopkeepers will quote them a suspiciously high price that, if paid, will produce something entirely different (and probably not at all legal). Have other NPCs entering the shops to ask, and turning it down in shops that are actually selling it, while going into a back room to "haggle" in the shops that are really selling something else. (But, you know, subtle-like.)

And swiped from the one actually fun mystery campaign I've played in - do it dinner theater style and have reasons why any shop could be either innocent or guilty, and roll with whatever the PCs decide. (Do not let them know you're doing this.) Mysteries always *sound* fun when you're planning them, but mostly I've seen them turn out frustrating in a hunt-the-pixel sort of way.

[Snarfmite]

And swiped from the one actually fun mystery campaign I've played in - do it dinner theater style and have reasons why any shop could be either innocent or guilty, and roll with whatever the PCs decide. (Do not let them know you're doing this.) Mysteries always *sound* fun when you're planning them, but mostly I've seen them turn out frustrating in a hunt-the-pixel sort of way.

Yeah, I was hoping to avoid giving the PCs a freebie, while still allowing them to have fun, gather clues, and solve the mystery. Can anyone else who's been in a mystery-styled campaign comment as to whether or not they end up being frustrating?