A Moral Dilemma

From the introduction: This adventure is designed for 4 to 8 characters of 6 to 10th level. The party should principally be of good alignments... at least, at the start of the adventure. ... The adventure starts when the characters are approached by Thallis. This can happen either by appointment— one of Thallis's henchmen or other allies arranges a meeting between his master and the player characters— or simply with Thallis walking over in an inn, or even in the street, and introducing himself. The DM should work some noteworthy action(s) of the player characters into the conversation as justification for their selection for this quest, if at all possible. However the meeting is arranged, both Thallis and any of his henchmen who might have been involved in arranging the meeting have their alignments and auras magically disguised, to such an extent that even a Paladin's innate ability to detect evil will not indicate anything amiss. This extends to all dealings the player characters may have with Thallis and any of his associates.