Cormyr: The Tearing of the Weave

"Cormyr: The Tearing of the Weave is the first-ever Forgotten Realms hardcover super-adventure! Designed to take characters from 4th to 8th level, the adventure pits the heroes against the evil agents of Shar and Cyric as they plot to corrupt the worship of Mystra, goddess of magic. The adventure begins in Cormyr, but the characters must also travel to the Plane of Shadow to thwart the villains’ machinations."

Summary
A new temple to Mystra has been built in the town of Wheloon. A traveling cleric of the Lady of Mysteries is overjoyed that his faith finally has a temple in Cormyr but when he goes to visit it he barely escapes with his life. He hires the players to investigate. Once inside, they discover that the priesthood is dominating magically adept supplicants and sending them into the Vast Swamp. Following the trail, they meet some lizardfolk who reveal that some of their brethren are being turned into undead and the dominated people go into a castle but never come out again. The undead guard the castle and the party has to fight their way through them to reach a portal to the Plane of Shadow. On the Shadow plane, they find a monastery and discover a plot by Sharran and Cyricist priests to create a huge area of dead magic. From there they descend into a canyon and battle their way through the native creatures of the plane to find Despayr, the Black dragon behind the entire plot. If the party succeeds, the Weave will heal itself, if they fail, Cormyr is in serious trouble.