After the Rebel Alliance managed to obtain the schematics of the Death Star, Vader was commanded by the Emperor himself to retrieve the stolen information. Vader received word of a possible Rebel courier en route to Kalakar Six, a volcanic moon once controlled by the Sith. However, there was no Rebel presence on the moon. Vader had been lured there by a cult of darksiders, who had managed to create a dopplegänger of Darth Sidious's previous apprentice: Darth Maul. They believed Vader's Jedi training had left him "tainted" and that only a pure Sith like Maul should rule at Sidious' side.
Both Sith Lords managed to hold their own against each other, until Vader managed to cut Maul's double-bladed lightsaber. However, both ends of the weapon continued to function, allowing Maul to use Jar'Kai against Vader, who had little defense against such combat style. Maul was apparently victorious, until Vader stabbed his lightsaber through his own body and into Maul's, fatally wounding him. Dying, Maul asked Vader what he could possibly hate enough to give him the strength to defeat Maul. Vader responded by saying it was himself that he despised.
Soon thereafter, Vader was met by the seemingly unsurprised Darth Sidious, who executed the treacherous cultists. When Vader asked how it was possible for Darth Maul to have been brought back, the Emperor merely replied that it was possible for that which was destroyed to be brought back again. The Emperor told Vader that the cultists were heretics, and they should resume their search of the stolen Death Star plans.
Behind the scenesEdit
The duel was selected as one of Star Wars Insider 83's 20 Most Memorable Moments of the Expanded Universe, with Leland Chee confirming its canonicity on his blog.