The Dustmen are a group of idealogues who seek to advance the world through the controlled development of new technology. They are fanatic, however, and very willing to take direct violent action against those who they believe are using technology for violent or tyrannical ends. The party has fallen into their sights through the development of several new kinds of alchemical and material weapons. They've managed to steal at least one variety of poison and the stake ballista from the party's workshops so far.
The party first engaged them in combat when a large group of them surrounded Alem's estate immediately after the party fended off the Chosen and found Alem dead. Using some of his old adventuring traps, the party was able to defend the estate, and drive the remaining Dustmen away.
Later, Neither Nor was able to track some of them down to a base in the old sewer system of Londolond. The party fought their way in, only to find them summoning a greater demon. The party was able to interrupt the ceremony, however, and spoke amicably to the demon before it dispersed.