Thanks for your suggestions, everyone! They were really helpful in getting my mind going along the right path. I just thought I'd report on how I ended up handling it.
I went with Iarno Albrek as the hook to get the party to Thundertree. I decided Iarno had stolen Gundren Rockseeker's map and gone to Thundertree looking to enlist Venomfang's help in taking over the mine operation from the Black Spider. So when the party rescued Gundren from Cragmaw Castle, they couldn't find his map. Gundren remembered seeing a wizard around the castle, and they also found a slip of paper with the words "Thundertree" and "Venomfang" on it. That gave them some investigation to roleplay, since they had to figure out what those words meant.
I'm posting a fuller writeup of how the session went in the Thundertree thread.
As a side note, the party was 4th level, but the twig blights and zombies were laughably easy for them. They negotiated with the dragon instead of fighting. I hope the mine will be more challenging for them.
I went with Iarno Albrek as the hook to get the party to Thundertree. I decided Iarno had stolen Gundren Rockseeker's map and gone to Thundertree looking to enlist Venomfang's help in taking over the mine operation from the Black Spider. So when the party rescued Gundren from Cragmaw Castle, they couldn't find his map. Gundren remembered seeing a wizard around the castle, and they also found a slip of paper with the words "Thundertree" and "Venomfang" on it. That gave them some investigation to roleplay, since they had to figure out what those words meant.
I'm posting a fuller writeup of how the session went in the Thundertree thread.
As a side note, the party was 4th level, but the twig blights and zombies were laughably easy for them. They negotiated with the dragon instead of fighting. I hope the mine will be more challenging for them.