The Cormyrian military reports that a Warforged Purple Dragon known as Orsican Grey goes AWOL for reasons unknown. War Wizard Acelynn Devereaux launches an investigation into his whereabouts. After careful clue-finding, adventurers discover that Acelynn herself has launched the investigation to track down the Warforged and silence him. On a mission to learn the secrets of the Warforged for nefarious masters, adventurers ultimately foil her plans and kill her. Orsican Grey is placed on trial for going AWOL but is cleared of all charges.
Planar travelers begin to whisper stories of Androlynne, the 471st Layer of the Abyss, and claim that Celestials there have finally put a crack in the curse upon that layer. For eons, Eladrin children have remained trapped thanks to a blasphemous pact engineered by Pale Night, but a group of adventurers find a clever way to temporarily pause the curse long enough to release a single Eladrin child. Stories vary wildly about how this was accomplished, and denizens of the Lower Planes claim that this was all a trick to give the Eladrin a delicious taste of hope so that it might be squashed again. Despite this claim, most Planar scholars and travelers believe this is a rare Upper Planar victory over the Lower Planes.
A brazen attack on Suzail leads to an explosion at the palace, with many dead, injured, or missing. Among the casualties, young Prince Azoun V is slain, and Mage-Royal Laspeera Inthre is gravely wounded and rendered comatose. Retired former Mage-Royal Vangerdahast returns to aid the Crown in its time of need. The attacker is soon identified as a Ghazneth - one of the demonically reincarnated traitors to Cormyr created by dark rituals at the hand of Nalavarathautoryl, the Devil Dragon.
Reports circulate, first in rumors behind closed doors and then more openly, of a looming threat within the heart of the Vast Swamp. Their worst fears are confirmed as an undead horde arises from the fallen land's lost ruins and secluded temples. Led by an ancient Netherese lich known as Vezzil, the Lich of Loss, the slow approach of the unliving army is heralded and shielded by a swirling, persistent magical storm of crimson Living Lightning conjured by arcane powers lost in the age of Netheril. These powers, thought to have been banned by Mystra, defy comprehension.
Attacks by undead forces and Fire Knives collapse the main line, forcing the Cormyrian "Purple Wall" into retreat. Soon after, a potent weapon known as "The Black" is revealed. This deadly toxin not only kills with the slightest exposure but renders the victim immune to all healing and any attempts at resurrection. The commander of Cormyr's military forces, Oversword Faril Laheralson, is laid low by treason, deception, and exposure to this deadly poison. For months, efforts to counteract this poison fail, and its demoralizing effect upon Cormyr's military is palpable.
The town of Thunderstone is utterly destroyed as Vezzil's army arrives. Before its destruction, Cormyrian forces placed experimental lightning rods to absorb the lich's Living Lightning. These rods prove effective, yet provoke the lich into utterly annihilating the Cormyrian forces. For the first time since the days of Netheril, the world watches in horror as Vezzil obliterates five thousand Purple Dragons and War Wizards with a casting of Tolodine's Killing Wind. The lands around Thunderstone become blighted by the spell. After the war, it takes years and extensive work by druids and adventurers to heal the land and reclaim Thunderstone.
Responding to the requests for aid, the Dwarves of Earthfast join the embattled Cormyrian forces, returning to the Forest Kingdom for the first time since the war against the Tuigan Horde.
Spurred by the movement of Vezzil's undead army through the Vast Swamp and approaches by draconic members of Cormyr's adventuring community, the black dragon Thaugloriacus "The Black Scourge" - eldest remaining grandchild of Thauglorimorgorus "The Black Doom," the very wyrm for whom the Purple Dragons are named - moves to enter the fray. A flight of chromatic dragons under his command descends upon Fort Morning Glory, a border fortress nestled against the Swamp's northern edge - where Purple Dragon forces, bolstered by adventurers and volunteers, had clashed with the front lines of Vezzil's forces. The dragons lay waste to living and undead alike, utterly destroying the fortress. A wave of anti-dragon sentiment rapidly burns through Cormyr in response. The Singers of Concordance, a group of metallic dragons and dragon-blooded adventurers, counteract these sentiments with repeated demonstrations of aid during the many battles of the war.
Vezzil attempts to breach through Thunder Gap and leave Cormyr from the east to devastate the elven communities of Deepingdale. Oversword Faril Laheralson defies the Regency's instructions to allow Vezzil through, declaring the Regency's actions cowardly and un-Cormyrian. Purple Dragons and adventurers hold his forces at bay with the now-finished gnomish lightning rods in a last-ditched attempt to bottle him in. Elven reinforcements from Evermeet and the Dales appear upon the field as Mage Royal Vangerdahast and "Love's Touch" Delshandra Goldenleaf, the elven head of Hanali Celanil's faith, join the battle in lockstep. Vezzil, rebuffed repeatedly by the heroic and defiant defense, lays Tolodine's Killing Wind over the pass. The arrival of a second Ghazneth - one friendly to Cormyrian forces - disrupts his attempt. The Ghazneth of Storms absorbs the entirety of the spell, preventing Vezzil from eradicating the defenders. For the first time in the War of Broken Crowns, the Lich of Loss is forced to retreat.
The aiding Ghazneth identifies himself as Rowan Cormaeril, husband of the late Princess Tanalasta and father of Azoun V. He continues to help Cormyr and its allies throughout the war, mainly from the shadows.
The Regency Council - at the advice of acting Mage-Royal Vangerdahast, Sage Royal Alaphondar, and Vangerdahast's estranged half-elven son and new apprentice Amaeldahast - secure the bastard children of Azoun IV after another falls to assassins' hands. With the death of Azoun V, three of these supposed bastards are gathered to be the prospective new heir to the throne of Cormyr: Vorndren Longlance, Tavantra Indimber, and Vaerun "Obarskyr." Leaving the war running to Oversword Laheralson's and Vangerdahast's command, the Silver Houses begin deciding which of the three should succeed the line of Obarskyr to avert political instability and potential civil war, primarily driven by fear of the current crisis.
The sources of Vezzil's unnatural power are finally discovered: The Dream Chamber, a mysterious power source that lurks inside the shattered citadel of Tyr'intor within the Vast Swamp, and a font of Whole Magic - raw arcane power said to be the remnants of Karsus' own weeping heart.
The elven theurge Kelendel Seleben, who foresees Vezzil's ultimate plan through the power of the Dream Chamber, enacts a desperate gambit to resurrect the one being he believes can match the Lich of Loss' power - Nalavarathautoryl the Devil Dragon. She collides with his forces and they battle to a standstill, with many of Vezzil's undead forces destroyed in their immensely cataclysmic, Weave-tearing magic.
Mage Royal Vangerdahast tasks another group of adventurers to locate and retrieve a globule of Whole Magic in a desperate suicide run. Using its power, Vangerdahast removes the curse keeping the comatose Crown Princess Tanalasta Obarskyr, eldest daughter and heiress of Azoun IV, in stasis following her near death during the Goblin War a decade prior. To the surprise and joy of many in Cormyr, Tanalasta is revealed alive and well. To the exhilaration of the country and a stabbing ray of hope amidst the darkness of the war, she is crowned the next Queen of Cormyr.
The bastard Vaerun - swayed by adventurers' influences - reveals his participation in the crowning selection of a scheme by his mother, the Red Wizard Brantarra, to place a puppet king upon the throne of Cormyr on behalf of the powers of Thay. Vaerun turns to Cormyr's side and provides valuable intelligence to the Regency Council, Vangerdahast, and the Purple Dragons. Brantarra withdraws from her public efforts under the guise of "The Herald" and retreats to her secured compound, where she is eventually tracked by the Purple Dragons and adventurer allies and slain in a vicious battle.
With Tanalasta's return, she has Rowan Cormaeril tracked down and, as Queen and speaker for the kingdom, forgives him. This forgiveness breaks the Ghazneth curse, restoring him to human form.
A raid on the Fire Knives's central compound in Westgate by the Harpers results in the death of the Fire Knives' leader, Tagreth Cormaeril. This shatters the organization and cripples any aid it provides to Brantarra or Vezzil. Several, if not all, of the participating Harpers are reported slain in the battle.
After retreating through the Wyvernwater, Vezzil's forces emerge once more near the city of Immersea, where they clash with the defending Purple Dragon armies, Earthfast Dwarves, Elven troops from the Dales and Evermeet, and numerous gathered adventurers. The undead forces are further harried by the arrival of Cormyr's old enemies, the Grodd Goblins of Nalavarathautoryl. The Devil Dragon takes the field and devastates many of Vezzil's forces, though the billowing storm obscures the extent of her involvement.
Vezzil's final forces and Cormyr's defenders come to a final head at the Battle of Redstone Castle in Immersea. With nowhere else to turn, the Lich of Loss emerges on the field in a desperate bid to slay the new Queen of Cormyr. After a vicious and deadly battle, Vezzil's reliance upon the power of the Dream Chamber runs its course. The lich, weakened during the struggle, is drawn into the Dream Chamber in an eruption of light and magic. With his destruction, the War of Broken Crowns comes to an end.
Following the battle, Nalavarathautoryl disappears in a westward flight. The Grodd Goblins bleed away into the trees. Though many believe the Devil Dragon has not forgotten her hatred of humans or Cormyr, her attention turns elsewhere for reasons unknown.
In the wake of the war, the Wyvern Crown of Cormyr - last seen in Vezzil's possession - is recovered from the battlefield in Immersea, only to disappear again almost immediately. A Purple Dragon soldier arrives at the gates of Suzail a few days later, transformed into an undead with a chilling message for the Forest Kingdom: the Crown is now in the possession of Sammaster Firstspeaker, master of the Cult of the Dragon.