Okay, I just got Half Dead City, and I find the motives of the Scorched Hand pretty weak. There's just not that much to it beyond "they really want to check out this temple, since it is dedicated to their god. And once they get there, they leave pass up plenty of loot. Why would there be any need for conflict with the party at all, beyond being angry at them as tomb robbers, which is the same thing they've been doing.
So in my campaign, the leader (whose ridiculous Pathfindery name will be truncated into something less of a mouthful,) is here because she had a vision. She saw a great threat to the world, and more importantly for clerics of Nethys, a great force of magic that will arise from that temple. In her vision, she saw a golden mask. She came here to stop the mask from falling into the wrong hands, which she quickly decides the is the party.
A lot of people have been commenting that they wish there was more contact with the rival gang, and this will accommodate that desire. Instead of waiting in until after the first day's exploration to introduce the other groups, I'm having them all sitting around in the tavern before the lottery. They will befriend the leader of the Dog Soldiers, who will act as a source of exposition and local color. I am having the lottery reveal all three assignments at once, and all three scrolls handed out. But parties MUST complete their first assignment before moving on (the priesthood numbered them all, and typical of bureaucracies, adhere to those rules dogmatically.)
When the Scorched Hand learns that the party has the Sanctum of the Esoteric Eye, they become agitated, and try to offer a trade, for all three of their targets (including a really choice assignment that promises to offer a lengthy delve.) The party should get the hint that they shouldn't trade, but if they do take the deal, the high priestess will tell them that the goddess chose these assignments, so they can't trade. The leader will curse at the players and stomp off.
When the final showdown occurs, the party comes across the Scorched Hand, who are about to open the sarcophagus. Here it could go either way. The party may parley with them, and they agree that the Scorched Hand will get to take the mask and leave. When they check the sarcophagus, the mask there is onyx, and she is confused, since the mask in her vision was gold. The party will tell her about the secret room with the statue and its missing mask, and she will realize that she has failed. This is a more upbeat ending, and she ends up not being a villain.
Otherwise, she will give them the story about the prophecy right before attacking (to keep them from bringing doom to the world.) Once she is dead, they will find the onyx mask and figure out she was misguided. Either way, this makes for a more interesting story in my opinion.
I know she's supposed to be return as a villain in the next book, so I might modify this plan when I read Empty Graves. Otherwise, I may pick another candidate for returning undead villain...