From the introduction:
The players hear from a legend that tells the tale of an ancient castle. The lord of this castle vowed he would defend the realm of any danger coming from the south (and in exchange married the beautiful princess, of course), but when danger came in form of an ancient red dragon sweeping to the north over his castle, he and his knights failed to stop him, thus breaking his vow. So they still roam the castle as spirits, void of voice, till they fulfill the vow. It is said that upon the right constellation of stars, the castle reappears and they have a chance to right their failure. Unfortunately, the dragon did not return, so still the castle reappears and the knights wait.
A system-neutral high fantasy adventure. Characters should be of medium power.