Quite a simple plot, but one that could be fitted in to almost any campaign, particularly one with a diplomatic or intrigue element.
A noble of the kingdom is suspected of having stolen state secrets, crucial to the defence of the kingdom. There is, however, no proof and the noble is sufficiently powerful that the government cannot have him seized and interrogated upon suspicion alone. The noble is currently travelling towards Esker, a medium sized city near the border of the kingdom - it is thought that he may have a contact here who he will pass the secrets too, and it is thus imperative that he not be allowed to reach Esker. The noble is travelling completely openly and has joined a merchant caravan (they are travelling together through a wilderness region for added protection from bandits). (Naturally, none of the above is common knowledge in the kingdom.)
The PCs are hired by the government to abduct the noble from the caravan, disguised as bandits. He can then be delivered to the government who will interrogate him, whilst making it appear that he has been seized by bandits for ransom. The catch is, of course, that the PCs must try not to kill anyone. This is not an order, but if your PCs are the sort who are being hired by the government, their morality will be such that slaughtering a group of merchants and merchants’ guards should be repungent to them. Destroying property as a diversion (such as starting fires) is a little better, but ruining someone’s livelihood is also not a very good thing to do. If they do accidentally kill people they should certainly feel appropriate remorse and act upon it in the future.
The PCs must also not be seen clearly. If they are, then this may cause serious problems: the merchant might, for example, post a reward notice for them. There is also the difficulty that a lot of the more intelligent things they could do (in terms of carrying out the abduction) are extremely morally dubious: for example, if they aided some real bandits to attack the caravan, the bandits would probably steal and kill at will. There could also be problems if the bandits refused to give up the noble (wanting to really ransom him).
Details of the caravan
Feel free to change these - they are merely suggestions.
16-20 wagons including:
Some carrying various goods of wood and metal.
Some carrying food.
Some carrying fine silk or some other material that will easily burn.
One carrying barrels of naptha (just to make things interesting).
Two of families travelling with children.
The merchant’s wagon.
Two or three wagons belonging to the noble: e.g. one for him, one for his servants, one for his guards.
A couple of guard’s wagons.
Number of guards (including the merchant’s and the noble’s) could be around 20. There might well be a few good warriors (for example the noble’s personal guard) (and the noble), but most wouldn’t be that good. Wizards and clerics appropriate to the magic level of your world. Definitely guard dogs, which should be able to smell any stealthy raiders.
The merchant is canny enough that if the PCs ask to stay the night with the caravan he will make them give up their weapons and will guard them. He is in bandit country after all. However, visiting the caravan could be wise to gain information.
The PCs must abduct the noble, silence him, and deliver him to the government (not too far away).
Don’t be afraid to play on the consequences - e.g. to do with morality if they kill people (they might want to try to secretly find out who that person’s family are and give them money to make amends), or consequences if they are spotted.
If you are feeling cruel, you could always make the noble innocent of treason. Then, when he is released, the PCs will have made a powerful enemy.