Just One More Thing...

With the dragon cult emissary in custody (presumably in one of the dungeon cells), attention is turned to the contents of his satchel. Most of his equipment is standard adventuring fare for travel in the wilds of the mountains, but there is also a collection of five scrolls bound together with a leather strap. Two of them are spell scrolls, Create or Destroy Water and Tenser's Floating Disc. The other three are sealed with a red wax embossed with a detailed image of a dragon.
All three are written in draconic (if opened for reading), but can be read with Comprehend Languages. If none of the characters have the spell, they can find it in a spell book tucked in among the papers of the acolytes. It can be copied into their own spell books, or cast directly as a ritual from the book.
The first scroll is a description of the destroyed shrine and the concern of the cult leaders that an important artifact had been taken. The instructions in the note were to locate a party of adventures matching your description, and to recover the necklace taken from the shrine. If there are any survivors, they are to be delivered to Drathkos, in the Molten Hills, along with the necklace.
The second scroll is a letter of inquiry, mostly conversational, but with two paragraphs of particular note. They mention the frost axe of Rain Thana (History DC20 (12 if dwarven) to recognize Thana as a mythical dwarven warrior and king who led a successful attack against a dragon and its army), and ask whether any news has been found to reveal its location. Somewhat scathing in places, the sarcastic tone suggests that the answer is already understood to be no, and the expectation is slight that they will. To this end, the intimation is that an adventurer capable of locating the axe is being sent along with a letter of recommendation. The third scroll is this letter, and vouches for the knowledge and ability of the emissary, Ference Trensal.
Ference Trensal is ranger, and has been sent because he knows these mountains well. He also is an expert of Dwarven studies centered on ancient kingdoms that once made their home in this area. He is reluctant to share any of his knowledge, but with charm, persuasion, or even outright bribery, he will. Defeated, he will need a long rest to recover his full health, and will refuse to answer any questions until he has had one. In all likelihood, he will feign incapacity until he has fully recovered.
Once questioned, he will try to avoid giving any information, but if pressed or otherwise convinced, he will give the location of a stronghold that he believes is the resting place of the fabled frost axe of Rain Thana. Unless successfully charmed (and overwhelmingly so), he will plot a path that exposes the party to difficulty and attack, though he will lead them to the stronghold in the end.
The stronghold is currently being held by something big... I'll think about that, probably giants of some kind.