In preparation for the undead attack, a small group of wizards (which included Antonidas) prepared a special spell that would do damage to any undead that entered Dalaran. The majority of Dalaran's citizenship was evacuated prior to the battle. Kel'Thuzad was able to sense the wizards and revealed to Arthas that the auras causing the damage to the Scourge would disperse upon the deaths of their casters. With a clear target in the mind for their mission of claiming the Book of Medivh, the Scourge began the invasion of Dalaran and quickly slew the first wizard and freed the first level of Dalaran of the aura harming them. Additionally, Arthas and Kel'Thuzad freed creatures that the Kirin Tor had caged for studying and that engaged the Kirin Tor in battle as well.
With their new unexpected allies in tow, the Scourge was able to locate the second wizard (who had hidden himself) and destroy the second Kirin Tor outpost in the city. With the outpost destroyed the Scourge began to ready themselves for their final push against Antonidas. However, while the first wizard was camped in the entrance of Dalaran and the second hidden (each with a few defenders), Antonidas had a whole army defending him as he kept up the final aura.
With no other course of action, the Scourge engaged said army in battle and after a fierce intense battle, the undead were victorious. Arthas, Kel'Thuzad and Tichondrius entered a vault where Antonidas awaited them. Although the battle was fierce, Antonidas was slain, and the Book of Medivh fell into the hands of Kel'Thuzad. Tichondrius also took the Skull of Gul'dan at the same time.
The Scourge moved to a hill outside Dalaran where Kel'Thuzad worked on the summoning spell while Arthas and his units defended him. The remnants of the mages had regrouped and now sent numbers of mages on the Scourge. The effort was ultimately fruitless as the demons were successfully summoned. In addition to various troops, the great Mannoroth and Kazzak were summoned as well. The summoning was complete with the coming of Archimonde who, moments later, razed the city's spires to the ground.