Night Watch: Murder by Magic

All the fabled Seers of Greyhawk have been killed on the same night, each by their own instruments of divination. And the only unusual sign is the ominous number of black birds in the skies of late. The mystery is dumped in the lap of Garett Starlen, commander of the night shift of the City Watch, who discovers that a web of evil has been tightly drawn around the great city.
As if murder by magic were not enough, strange beasts decend on the citiznery, and the powerful Guild of Wizards is vanguished by an unseen force. Can nothing stop the deadly zalots of the Horned Society?