Echoes Of The Well Of Souls

Nathan Brazil had been the guardian of the Well of Souls, where the Well World's master control lay. But now the universe faced a threat more grave than mere destruction: An unnamed and utterly alien entity had somehow been released from its ancient prison and was bent on the corruption of the Well World itself. If successful, it would cause chaos beyond mortal understanding....
From the Paperback edition.
The first book in a fabulous new trilogy set in Well World--site of bestselling sf mainstay Jack Chalker's most successful series of novels. For uncounted aeons, the Well World had given order to the universe. Now, an utterly alien entity was loose--and bent on corrupting the Well World.