Nice job overall, with a very good map and a bleak setting. It's a quite anticlimatic in the overall layout, but a willing referee can work it out... yet they shouldnt have to. 

Very solid visual design and gameability, this can be dropped in basically any setting with very little effort. The theme is nicely played and I like the idea of this being both an investigation and a rescue mission.

It gets a bit weak on the actual citadel, though. The PCs are expected to be discreet but there’s no reason for them to: the citadel is full of still-loyal citizens (some of them armed guards) and the cultists cannot interrupt their ritual, not even to kick the PCs, without losing. It would have been better if the citadel was controlled (or reportedly controlled) by cultists, giving the PCs a good reason to fear discovery.

I like the overall setup and premise here. The thunder and lightning (and associated hazards) effectively set the atmosphere, the oblivious guard is a nice touch, and your NPCs are distinct and well-thought out.

You've got a pretty well-appointed town considering it just burned down, though. I also don't understand how the King's daughter plays into this. Also, if the cult has already taken the citadel, why allow business as usual around town? The town should be crawling with cultists. I wonder how it would feel if this infiltration mission happens before the citadel is attacked. The party gets sent to investigate the sudden unexpected storm at the town, people are scared, Storm-Spawn keep appearing, three weirdos are in the inn's attic. At midnight, the storm will reach its peak, the town will burn, and a contingent of cultists will take the citadel. Maybe Lythen or Kip have noticed some folks gathering in the woods. Now the party has a chance to save the town, the citadel, and the princess. If they succeed: Kudos, but now the party has made an enemy of Storm Cult. If they fail: its now time to storm (ha!) the citadel and save the princess.

Clean layout, good use of an existing map, and well-described town. It just didn't match the premise of the background.

I like the premise. Using a storm to keep the adventurers contained is a good idea.

I'm assuming you are using Dungeons and Dragons based on the references to the monster manual and some of your terminology, but I don't see it written anywhere. You may want to do this so that GMs know what system they should prep.

You mention that the citadel is evacuated, yet there are quite a few people here. 

Why do the PCs need to do their job discreetly? What happens if they are caught as outsiders? If they were hired by the king, why would the guards care?

What happens at midnight? Do the wizards finish the ritual? What happens if the PCs fail to stop the ritual?

Great map and amazing cover... I love how the the crack almost looks like a thunder bolt. 

A tense situation for detectives and defenders alike. Great cover & nice weathering!