The PCs are passing through the village of Harrowglen during the day of a large fair. As they enjoy the sights before their trek out into the wilds, they spot a tower that appears be climbing over a hilltop. Among screams of the locals, the tower continues its advance, massive spider-like legs supporting the tower as it crawls towards the village. As it nears the fair, the tower disgorges a flock of vargouilles, which shriek and dive on the villagers. It is up to the PCs to stop these vargouilles, then enter the tower and stop its diabolic master before the massive construct can continue its rampage!