A One-Round Living Greyhawk Gran March Regional Adventure
From the introduction:
Watcher Corum Valstier has been kidnapped by some unknown enemy of Gran March masquerading as a fellow knight. The fiend has brazenly called out the Knights of the Watch, the Church of Heironeous, and heroes of Gran March at large challenging them to catch him if they can. Following the creature's trail should be no problem as it begins a cross country trek from Orlane to points east leaving a trail of chaos in its wake. Catching it and rescuing Valstier, however, may prove more challenging.
A Gran March regional adventure for [character levels] 6 - 12, and Part Four of the "Outsiders In" Series.