Battle for the Tantalus Eye

The Battle of the Tantalus Eye was a major battle fought during the Last Great Time War and one of its last. Its fallout was immense as it convinced the War Doctor to destroy both the Daleks and the Time Lords to save N-Space from further damage. (PROSE: Engines of War, The Whoniverse)

Landing on Mouldox
After being attacked by Dalek stealth ships, losing an entire Battle TARDIS fleet to the Daleks, the War Doctor crashed on Moldox, meeting the rebel fighter Cinder. Though she was initially hostile to him for being a Time Lord, she warmed up to him when he offered her passage off Mouldox and away from the Time War. Upon being informed that the ruling Daleks, a group called the Eternity Circle, were rounding up humans as prisoners instead of exterminating them, a suspicious Doctor convinced Cinder to investigate the Dalek base, discovering the Temporal Cannon, a weapon capable of temporal dissolution that the Daleks intended to both mass produce and fire a large scale version at Gallifrey itself. Upon securing a Cannon, the Doctor and Cinder left for Gallifrey.

Granted an audience with the High Council, the Doctor informed them of the threat with deciding to use the Tear of Isha to close the Tantalus Eye and deny the Daleks the power source they needed, uncaring that this would cause the death of trillions of humans living there. Furious at the plan, Rassilon's treatment of Borusa and the Time Lords' treatment of Cinder, the Doctor swore to stop it, prompting Rassilon to arrest him. (PROSE: Engines of War)

The Battle
Commander Partheus was dispatched to lead an armada to the Tantalus Eye and deploy the Tear. On Gallifrey, the Doctor and Cinder managed to escape custody and reclaim the Doctor's TARDIS, though having to evade five Battle TARDISes and more Dalek stealth ships. Before they made for the Tantalus Eye, the Doctor brought his rival Karlax aboard, allowing him to regenerate.

Setting course for the Eye, the Doctor and Cinder arrived on Partheus' TARDIS, hijacking it and deploying the Tear at the end of the universe. With no weapon, the Time Lord armada retreated from the area. Concurrently, the Doctor returned to the Death Zone, retrieving Borusa, since turned into a possibility engine, for his help in stopping the Daleks.

Arriving in the Tantalus Eye once again, during the final stages of the Daleks' construction, the Doctor surrendered himself to learn more about the weapon and the Daleks' plans for him. Upon learning that the Daleks intended to transform him into the Predator Dalek, the TARDIS materialised around the Doctor and Cinder, piloted by the regenerated Karlax. Knowing Karlax would betray him, the Doctor had set the ship to home in on Cinder's tracking device if someone but him worked the controls. Furious, Karlax tried to kill the Doctor only for Cinder to take the shot. Enraged, the Doctor dematerialised without Karlax, leaving him to the Daleks.

Following Cinder's death, the Doctor realised that Borusa's powers had been augmented by the Tantalus Eye and he could make possibilities into reality. Though Borusa confirmed that he could make real a world where Cinder lived, the Doctor realised that doing so would squander the chance to stop the Daleks, the chance that Cinder had died for. Instead, the Doctor asked Borusa to erase the Dalek presence in the Eye, the former President of the High Council doing so and contentedly dying from the overexertion. (PROSE: Engines of War)

Legacy
President Rassilon officially declared the Doctor a traitor and exiled him from Gallifrey. (PROSE: The Whoniverse) In the aftermath of the battle, the War Doctor returned to Mouldox and observed the people rebuilding. Though their memories of the Daleks had been erased, he was quite sure that they would eventually return. The Doctor spent three days tracking down what had been Cinder's home before the Dalek invasion, exhuming her family's remains for a proper burial alongside Cinder. After honouring his friend, the Doctor promised "No more", resolving to end the Last Great Time War. (PROSE: Engines of War) In the last days of the conflict, he used a stolen gunship to burn this pledge into the Dalek City, (PROSE: The Day of the Doctor) and carved it into a wall during the Fall of Arcadia. Having declared his intent, the Doctor proceeded to steal the Moment from the Omega Arsenal, with which he planned to destroy the Daleks and Time Lords together. (TV: The Day of the Doctor)

Following the Time War, the Ninth Doctor was drawn into a trap for his memories on Nomicae. When the orbiting fleets began fighting, the Doctor projected his memories of the Time War into the various adversaries battling for access to his mind, among them his grief when Cinder had perished in the Battle for the Tantalus Eye. This memory, among others, caused the duelling to cease, as the combatants found them too terrible to bear. (COMIC: The Bidding War)