Not too long ago, a trade ship holding livestock moored at Harbat harbour. True prize-beasts they were, and the herders from the Goblin Islands desired to acquire some of these calves, which would - given time - increase the value of their herd considerably. They lent a sum of a thousand gold from the tax collector. A golden deal! The tax collector would be repaid in threefold, the herders would gain more from their animals, and the butchery would yield meat of the highest quality.
Alas, the stupid hillmen were cheated out of their coin, and now have a debt unpaid with the tax collector. Stubborn and honorful as they are, they have turned against the authorities (acting violently and throwing mud at anyone mooring at the Goblin Islands). Now, the tax collector can't very well round up an entire population and ship it off to the prison: people need their meat and their herders, the latter preferably alive. But since he is a man with a strict policy he can't let the insult go unpassed either.
Therefore, he has been looking for a band of adventurers to settle the matter. He wants them to take ship to the islands and impose as evil wizards or usurping tyrants, frightening the cattle and exploiting the herders' pagan superstitions to turn them back towards the authorities. Apparently there is a deserted castle on the island which would do very well as the home of a dark sorcerer. Once moulded thus with fear, the tax collector could easily sweep in with a small army and impose some harsh new settlements. And that's that.