Burrow, you were present when the group assaulted the Citadel of Broken Souls with Sir Praetol and found the documents concerning the baatezu's discovery of a creature known as the Maeldur. Your research, however, took you in a different direction from that of your friends. Intrigued by the unnatural disease that affected the paladin and members of his army, you delved into the dark of that instead, trusting in the ability of the rest of party to deal with whatever malefic plans the fiends are laying.
In last few weeks, you and the priests of Qua-Nosham have learned some interesting chant about the strange malady, though its nature has still not been made fully clear to you. Like the fiendish gutworms you study, it is a parasite of some sort, feeding preferentially off lawful hosts and draining away their will and sense of identity. Curiously enough, it is not fiendish in origin, though it is somehow sentient. Sir Praetol and his men eventually slipped into a Gray Dream, their minds ensnared by an alien mental influence, from which they will never wake unless a cure is found. Alas, you have uncovered all you can about this newfangled pathogen-- it is time to leave Qua-Nosham and search for more answers elsewhere.
Planewalking is a hazardous activity for a lone adventurer, even in the best of times, so you are seeking to join up with your fellow party members. The last missive you received from them (a couple days ago) stated that they were planning to visit Torch, in search of a possible lead. By the time you got to the Ubiquitous Wayfarer though, they had already left. Cursing the lousy Sigilian traffic and the sodding Hardheads that had closed off several blocks worth of perfectly decent streets on account of some altercation with the Defiers, you make your way to the Market Ward, to take the same portal they had (hopefully) taken not so long ago.
So here you stand at the mouth of an alleyway near a small tool shop, your planar sense alighting on the telltale glimmer of a portal a few feet away. A dusty, faded sign in the shop's window reads "portal keys and maps sold"-- a good thing, considering you have no clue what the key is.