Lots of great responses here--thanks!
My players--all 2nd level, a thief, a dragon shaman, and a bard/beguiler multi--are "part of" (read: "being blackmailed by") their local thieves' guild, which provides "assignments" (red: "heists") to them.
Their next assignment is to travel to a southern city (Greyhawk in the adventure, although I'll change it's name to fit my campaign) and discover how close the gang in that city is to finding a cure to their malady, and prevent them from finding it, if possible. (Darn rivals!)
Their contact will be in a tavern which, co-incidentally, will be across from the locksmith's shop as the two sneaks are leaving, and thus the adventure begins...
I hope three 2nd level PCs will be able to handle the challenge...they have a scroll tube, magically enchanted to send messages and potions from the guild to the PCs and back. The guild "emails" them healing potions as requested.
One of their heists will be to steal the "journal" (read: "alchemy book") of a witch, so that the guild can create healing én mass.