The Darklight Sisterhood is Cheliax's answer to the Pathfinder Society. Because both Cheliax and the Society seek to acquire ancient relics and uncover lost secrets (though for vastly different reasons), the two are in constant competition. Pathfinders tend to receive more goodwill from locals throughout the world because of their reputation, but their Chelish counterparts don't get the same level of assistance. As a result, the Darklight Sisterhood was formed to counteract Pathfinder activity more covertly.
This society of adventurous women, many of whom are or were Pathfinders themselves, is loyal to Cheliax, and operates as a network of government-sponsored spies. They report not to a local chapterhouse, but to their superiors in Cheliax. The Sisterhood has its strongest presence in Cheliax proper and its former imperial holdings. The organization is much smaller than that of the Pathfinders and the competition between them is relatively one-sided, so their existence is not even known to many Pathfinders, save those of high rank or who have encounter the Sisterhood firsthand.
Upon joining the Sisterhood, a woman changes her last name to Darklight in a symbolic marriage to the Sisterhood. For those in the know, this is the easiest way to recognize one of the organization's members, as they have no other distinguishing marks or denotations of affiliation. This renaming has no impact on whether a Sister can take a husband, but she must not change her name from Darklight.