Gossamer & Spidersilk

From Glen Cook Wiki

Gossamer and Spidersilk are twin sisters, minor sorcerers from Charm--Imperial wizards who seek to emulate the Ten Who Were Taken in style. They dress in a menacing black outfit and mask. They are not nearly as powerful as they pretend to be, being perhaps a small order of magnitude above Goblin and One-Eye, if that.

The two sisters are sent to Oar to help rebuild the city after the Limper damages it, but soon realize that the Silver Spike is hidden somewhere in the city. The two scheme to get their hands on the Spike, lusting after the dark power it represents. In doing so, they allow the city to descend into chaos.

They continue to scheme even after Charm sends higher-ranking officials, undermining the efforts of their own people and eventually getting killed for their trouble.