The Shadow Thieves is a thieves' guild based in Athkatla, a large port city in Amn. They were formerly the most prominent thieves' guild in Waterdeep, but have since been all but routed from the city by the Lords of Waterdeep. It is alleged they currently have some arrangement with the Council of Six, as the merchants of Waterdeep are the main trading enemies of Amn.
The Shadow Thieves are ruled in Athkatla by a group called the Shadow Council. Marune "The Masked", who reports to the Shade of Baldur's Gate, thereby the entire Shadow Council, leads a sect of the guild still operating in Waterdeep.
The Shadow Thieves began to operate in Waterdeep in 1255 DR. After the guild was infiltrated by Lhestyn, a Lord of Waterdeep, in 1298 DR, it was destroyed, its leaders were unmasked or killed, and the Shadow Thieves were banished from the city. They resettled in Athkatla. They have since grown to be one of the most prosperous thieves' guild in Faerûn. With the exception of Waterdeep, they currently hold the lion's share of criminal activity along the Sword Coast and Amn.
Ever since their expulsion, the Shadow Thieves have long attempted to reestablish themselves in Waterdeep. Until around 1372 DR it had been the constant vigilance of the Lords of Waterdeep to keep the guild at arms length. As Waterdeep fell on hard times, the Shadow Thieves got an opening they were quick to exploit. For over five years, the guild has slowly come to dominate criminal activity in the docks, southern and trades wards with the northern ward of the city being at risk as well.
In 1370 DR, Marune unveiled a grand scheme for giving the Shadow Thieves an unassailable edge over the Lords of Waterdeep. The necromancer began distributing slippers of shadowwalking to the guild's highest-ranking thieves. These agents of could then effortlessly navigate Waterdeep's shadows, beyond the reach of the city's Lords.