A large predatory mammal that can run or fight on two legs, not requiring sleep these demons were brought onto the world to create killers, in the world of werewolves these could be considered alpha males.
This oily, crimson liquid is rare to find even in the more complete apothecary’s collections. It can be easily applied to any blade or arrowhead as it was designed to do so, however if consumed it will have no ill effects on the drinker.
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?