From the publishers blurb:
Deep in the jungles of Xen’drik, embedded in the side of a mountain stands the tower of the Mad Mage Xeffon. Though his various servants can be found flowing in and out of the tower on a daily basis, the elusive wizard has not been seen in many years. Some say he no longer lives, while others postulate that he is locked up in his laboratory, tinkering with magics that could alter the face of Eberron! Learn the truth in this supplement for the World’s Greatest Roleplaying Game!
The Mad Mage of Xen'drik includes:
A new location suitable for campaigns featuring tier II characters
Rules for manifest zones which can also be adapted to planar travel in Eberron
A new magic item: Orrery of the Planes
A CR 17 NPC: The Mad Mage Xeffon