|“|| What could bring heaven to the depths of hell?
Aliisza betrayed her lover, her mentor, and her son in order to try to stop the dark plot to kill the goddess Mystra. She failed. Now the goddess is dead, magic is malfunctioning, and Aliisza and her companions are trapped. Her only hope of escape lies is in convincing the angels and demons she just betrayed to trust her and work together—before they kill each other.
What Aliisza has witnessed has changed her forever, but that's nothing compared to what happened to the multiverse itself. The startling climax will change the nature of the cosmos forever.
Having failed to prevent Cyric and Shar from stealing Azuth's staff and slaying Mystra, the goddess of magic, Aliisza, Tauran, Kael, and Kaanyr Vhok must deal with the consequences in a multiverse reeling from the chaos of the gods and the Spellplague. The four, along with the now-soulless Zasian Menz and the merged abomination of Micus and Myshik Morueme, are trapped in a shrinking bubble plane connected to a dying planetar. Micus-Myshik turns on the others as, and Vhok manages to fend off the kraken and knock out Micus-Myshik while Zasian keeps the planetar alive.
They soon end up in a remnant of the Blood Rift, where they are captured by a hoard of demons besieging a horde of devils as part of the never-ending Blood War. Leaving the others, who are wounded, behind, Aliisza and Vhok ally with the demons' leader, Vhissilka the marilith. In exchange for free passage, they agree to help Vhissilka fight the horde of devils.
Meanwhile, the celestials in the House of the Triad are trying to keep order and separate the many creatures who were merged when magic went awry. They notice that in addition to the disappearance of the World Tree, the plane itself seems to be shrinking. The diviner Eirwyn, previously imprisoned for aiding Tauran against the orders of the High Council, is pardoned and sent to the seer Erathaol in Xiranthador in order to help sort out the mess the gods are making. She has visions of a crystal mountain that she cannot find, but soon decides the visions are of a location that exists in the future only.
Aliisza and Vhok return to their group and find Tauran awake at last. Upon Vhok's insistence, Tauran frees him from the geas that forces him to serve the angel. Vhok then escapes on his own, leaving his former lover and her friends to fend for themselves. The devils move upon their position, but Aliisza, suffering from the Spellplague, is unable to conjure a magical portal to safety. As a last chance of escape, she takes Pharaun Mizzrym's desiccated finger from the hilt of her sword and uses it to confer Pharaun's soul into Zasian's body. Pharaun is then able to use his magic to help himself, Aliisza, Kael, and Tauran escape.
They escape, only to find Eirwyn and other servants of Tyr already there waiting to bring them to justice in the Court of Tyr. They are imprisoned and sentenced to the following fates: Kael's custody is to be given to a new tutor; Pharaun is to be banished from his borrowed, "imperfect" body; Aliisza is to be banished from the plane; and Tauran is to be stripped of his immortality and banned from the House of the Triad.
In the meantime, Vhok has allied with the balor lord Axithar, who plans to invade the House of the Triad with the help of Vhok's inside information. The angels learn that Tyr has resigned his godhood, turning over his worshipers to Torm. The angels struggle with their conversion as the demons invade. Garin and Nilsa lead the celestial armies while Tauran, Aliisza, Kael, and Pharaun are freed to help defend the House. They lie in wait at the Lifespring, knowing it is Vhok's target. Vhok appears with Micus-Myshik in tow. Kael slays Micus-Myshik and a glabrezu; Pharaun gives his life to protect Kael from backlash from the glabrezu. Vhok slays Tauran, but Aliisza summons the last of her magic and life energy to slay him.
The demon horde is defeated when at last the legions of Bahamut appear, but the House of the Triad is left in shambles. It will be rebuilt as part of Celestia. Kael, bereft of his new-found family and no longer feeling he belongs among the angels, goes off alone to discover himself.
- Aliisza, alu-fiend and Kael's mother
- Kaanyr Vhok, cambion warlord
- Kael, half-drow paladin of Torm
- Tauran, astral deva servant of Tyr
- Axithar, balor lord
- Eirwyn, astral deva servant of Helm
- Garin, angel servant of Tyr
- Micus-Myshik, melded astral deva/half-dragon abomination
- Nilsa, astral deva servant of Tyr
- Pharaun Mizzrym, drow wizard
- Zasian Menz, priest of Cyric
- Vhissilka, marilith
- Erathaol, paragon archon seer and ruler of Venya
- Grezkith, molydeus
- Oshiga, trumpet archon
- Viryn, solar
- Astral Sea
- Blood Rift remnant
- House of the Triad/Celestia
- Xiranthador, Venya, Mount Celestia
- Dweomerheart (mentioned)
- Prime Material Plane/Toril: Hellgate Keep (mentioned)
- World Tree (mentioned)
- Astral kraken
The Crystal Mountain is also available in The Empyrean Odyssey omnibus.