Tumbleweir is a pleasant-looking village, in Femphrey, lying in the shadow of a huge dam at the end of an equally pleasant valley of managed woodlands and green wheat fields. The dam was built by Dwarfs centuries ago and there’s no-one left, who knows how to open the sluices, which are connected to a series of valves. They daren’t try opening any of them in case they make a mistake and flood the village. They could probably be worked out by a cunning mind with enough skill and some luck.