If you’re looking for a one-shot Dungeons & Dragons adventure, might I recommend Nameia’s Laboratory? I have not been able to play it yet, but it looks so good. It’s designed to take a party of 4-6 level 6 characters roughly 4-5 hours to complete, and the beauty is that it’s designed so that you can use this to launch the next part of your story in your own campaign if you want, but it doesn’t have to. Honestly, I’d love to see author Stratos Fotakis use this as the first part of an adventure exploring the Crimson Order. I don’t want to spoil anything, but here’s the synopsis:
I do want to note that the lovely artwork is from Alexandros Balatsouras. You can purchase Nameia’s Laboratory on DMs Guild for $2.95.