The Opal Tribunal is one of the most mysterious organizations of the Tessah Archipelago. There is evidence that the organization has existed since the area was first settled, and that few historical events have transpired without the influence of it’s shadowy courts. The Opal Tribunal selects their Jury seemingly at random, delivering simple written instructions to those individuals they have selected to enact their will. Disobeying these instructions, which often instruct their recipients to risk great danger and travel huge distances, will result in a swift death at the hands of the Tribunal. Our adventurers hail from all corners of the Tessah Archipelago, brought together to bring justice to the cutthroat world of Sur-on-Mur’s docks.

Sur-on-Mur is one of the busiest ports in the Tessah Archipelago, and the unquestionable economic center of the Korr region. Among the legions of merchants and traders whom call the city home, Arlato Atir, a tiefling shipping baron, is the lord of the docks. When the body of his only daughter is discovered on the shores of a distant beach, Arlato offers half of his estate to the individual who brings him the head of her killer. However, there is a problem: about half of the population of Sur-on-Mur has some sort of grudge against Arlato.

After that, take a look at your wiki. There is some more helpful info there.
http://www.obsidianportal.com/campaigns/opal-tribunal-murder-at-the-docks/previews

Opal Tribunal: Murder at the Docks