When Darth Maul Fought Darth Vader

It happened in Legends, on a volcanic Sith moon called Kalakar Six, in the year the Death Star plans went missing. A cult of Sith fanatics resurrected Darth Maul and set him on Vader to prove that a pure Sith belonged at Sidious' side. Maul had Vader on the floor. Vader ended it by summoning his lightsaber and driving the blade through his own stomach into Maul behind him. (Star Wars Tales 9, "Resurrection")

How Vader ended up there#

The setup is almost mundane. Shortly before the Battle of Yavin, with the Death Star plans in Rebel Alliance hands, word came through that Rebels were passing the stolen schematics on the volcanic moon Kalakar Six, and Darth Vader went to intercept. (Star Wars Tales 9, "Resurrection")

Sensing something familiar as soon as he landed, he sent his stormtroopers ahead. A red-bladed assassin cut them down. (Star Wars Tales 9, "Resurrection")

What he found inside the volcano was not a courier. It was a group of Sith fanatics called the Prophets of the Dark Side, who told him the Rebel information had been false all along. They had brought Darth Maul back from the dead, and the thing standing in front of him was solid, armed, and every bit the duellist the original had been. (Star Wars Tales 9, "Resurrection")

Maul's argument#

The Prophets had a reason, and Maul agreed with it. In their view Vader was not of the blood of Bane, his years inside the Jedi Order had tainted him, and only a pure Sith deserved to rule beside Sidious, and Maul had been that Sith before a Padawan on Naboo cut him in half. He had come to take the job back. (Star Wars Tales 9, "Resurrection"; The Phantom Menace)

That belief was not baseless. The Prophets saw Vader as too much of a Jedi to ever truly commit to the dark side, and Sidious had already toyed with a version of the same idea himself, inviting Starkiller to kill Vader and take his place. Maul was not fighting for revenge here. He was fighting for a position he thought was rightfully his. (Star Wars Tales 9, "Resurrection"; Star Wars: The Force Unleashed)

The duel#

They were equals for most of it, trading insults as they fought through the volcano and out onto a bridge over a river of lava. The bridge collapsed under them, and both barely escaped the fall. (Star Wars Tales 9, "Resurrection")

Vader got the first real advantage, cutting Maul's double-bladed lightsaber in two. Maul turned that into an upgrade, since both halves still worked, and fought on two-handed until he struck Vader across the helmet and knocked him to the floor without his lightsaber. Maul stood over him, certain of the win. What came next is the moment that gives the story its bite. (Star Wars Tales 9, "Resurrection")

Vader summoned his lightsaber back through the Force and drove the blade through his own stomach, killing Maul behind him. Dying, Maul asked what Vader could possibly hate enough to destroy him. The answer was one word: "Myself." He used the one thing he had that Maul did not, which was a total willingness to destroy himself to win. (Star Wars Tales 9, "Resurrection")

The Prophets, in a technical sense, were right about Maul. He did beat Vader. He just did not survive being right, and neither did they. (Star Wars Tales 9, "Resurrection")

Palpatine turns up#

When Vader turned on the Prophets, Sidious was already there, and it was his lightning that killed them. He said he had come to check on his apprentice's progress and denied any part in the plot. Whether Palpatine arranged the resurrection or simply let it run, he was close enough to watch the whole thing. (Star Wars Tales 9, "Resurrection")

That relationship is the real story here. Sidious got a data point on how far his apprentice would go, and Vader got a reminder that his master would happily watch him nearly die to find out. (Star Wars Tales 9, "Resurrection")

Sidious told him there was much still to do about the stolen plans, and Vader followed him to the shuttle. The hunt took him to a Corellian corvette called the Tantive IV and a captured senator from Alderaan, and the rest of that story is well known. (Star Wars Tales 9, "Resurrection"; A New Hope)

Where this sits in continuity#

This is Legends, not current canon. The duel comes from the short story Resurrection in Star Wars Tales 9, part of the old Expanded Universe that Disney set aside in 2014. Even its Legends standing is shaky: Star Wars Tales often ran stories outside continuity, and StarWars.com has since described the events of Resurrection as non-canonical. (Star Wars Tales 9, "Resurrection")

Current canon takes Maul somewhere else entirely. He survives Naboo, rebuilds himself, and dies on Tatooine at Obi-Wan Kenobi's hand in 2 BBY without ever meeting Vader as an equal. The Legends version, where the two most feared duelists in the galaxy actually cross blades and one of them wins by stabbing himself, only exists in the old continuity. It is worth reading anyway. (Star Wars Rebels, "Twin Suns")