"Got this here from a wizard on a bargin. Just the thing to survive the salvaging of treasure from the deep when you don't have a lot of start up cash. Not everyone can tame sea turtles mate, you know what I'm saying? This here is an item with it's own character, a real unique item, so beware of imitators! The surest way to spot a fake is have a friend try it, if he dies, all you have is a ordinary bucket and a funeral to pay for, this here is the one real deal you've been looking for and it's still available for a steal!"
- Street hawker outside the Affordable Arch-Mage
A simple metal bucket, capable of holding a bucket of water, or as it happens, a lifetime of effort.
After the PCs defeat (or force the rapid retreat of) a villanous necromancer/demon summoner, they discover a book. This book outlines how to summon a demon whose power increases according to the size of the summoning circle used to summon it. And after the PCs examine a map of the country, they find that the layout of the cities and roads match up with the required summoning circle. In fact, the final road that would complete the circle is currently in construction.
With anyone who can find out about the circle and the ritual to summon the demon able to somehow make the final road/line, and destruction of the cities and roads currently in existence out of the question (unless this is an evil campaign- that removes the moral quandary), how are the PCs going to solve this problem?