Caravans travelling through the desert have been disappearing. Doesn't matter which desert, pick any suitable one in your campaign world. The backstory for the DM explains why, with a neat twist that makes it something out of the ordinary, and there are a few hooks to attract the party's attention - some will do even if they are quite a way from the desert in question (you could even have other adventures on the way there if you wanted!).

Asking around at whichever end of the caravan route the party finds itself will pay off, there are quite a few snippets of information for them to gather. Eventually, however, they will have to venture forth onto the desert sands and all the accompanying dangers of extreme heat, dust storms, etc. There's a rare botanical treat here too - a cactus treant! Somewhere along the route, the party will encounter the location of the attacks and if they are lucky, the base used by the attackers.

There are some interesting and unusual possibilities for further adventures based on what is actually going on should the party try talking rather than rushing straight in to a fight... but plenty of opportunity for a good brawl if that's what they are after. The ramifications of variois actions the party may choose to take are also discussed, which could also lead to follow-up adventures.

Overall, a neat little adventure with scope to develop into a major plot point in your campaign if you wish, or just to be another job in the party's adventuring career if you prefer.