The group turns and looks outside the museum and there's a man there wearing cultist robes. He's looking around confusedly. If he notices the player characters, he waves and walks to meet them.
This man is Kevin ("Brother Sandtrap"), and he's a terrible cultist. He was inducted into the cult just last week, mostly on the basis of having a lot of money they wanted to get from him. He received a message this morning from Brother Sunwyrm, saying that there were artifacts of tremendous power, and the group was going to meet behind the City Hall and retrieve the artifacts and achieve their Destiny, and that there would be a 50gp fee for this Destiny.
Rather than showing up behind City Hall, Kevin has gotten confused and is standing in front of City Hall, wondering where everyone is.
As the group gets close to Kevin, he waves confusedly. "Oh, hello!" he says. "Are you here for the meetup? To achieve our Destiny? I brought the money."
Kevin is extremely gullible. If the group tries at all to get information out of him, Kevin happily explains everything he knows about the cultists and their plot.
"Oh, yes, they're very nice people! I met them a week ago through Brother Sunwyrm, and after I paid the initiation fee, they told me I could be a cultist too! They all call me Brother Sandtrap, which is a name that I chose for myself! I've always thought that I was better than everyone else, you know? Really, I'm destined for great things! And Brother Sunwyrm -- his real name is Jason, but he likes to be called Sunwyrm -- he says he can help me realize that destiny, through the glory of Teemat! I pledged my soul to him, did you know?"
"And they gave me this! It's a relic of Teemat! It lets me shoot fire -- look!" (It does, in fact, let him shoot fire like a blowtorch.) "We all have them! It's how you know we have a Great Destiny! And this morning I got a message about even more Destiny! Apparently the museum curator has our Destiny artifacts, and they're what made the ancient draconians so powerful! And now they're going to be ours! Just as soon as I find Brother Sunwyrm. The message said we'd be meeting behind City Hall, so they should be there by now. I actually thought Brother Sunwyrm was with you guys. Do you know where he went? I have the money..."
An easy skill check might allow the group to notice the sound of chanting, in Draconic, coming from behind City Hall. There are several cultists standing back there casting some sort of ritual spell. This probably leads the group to Scene 6: Cultist Battle.