During the Clone Wars, the Galactic Republic launched a mission to destroy a Confederate listening post on the planet Vanqor. However, the Jedi Master Quinlan Vos, who was secretly working for the Separatist leader Count Dooku, leaked intelligence about the operation to the Separatists. As a result, the Separatist were able to evacuate the listening post well before Republic forces arrived. When Republic forces and Jedi forces arrived, they found that the listening post had already been abandoned. As a result, the Jedi Order came to suspect that they had a traitor within their ranks.
Quinlan Vos (pictured) found himself a double agent in the Clone Wars.
Following a failed Jedi and Republic operation to extract supplies from a Separatist supply storage base, the Jedi Master Quinlan Vos was praised for saving his Jedi comrades by warning them about the presence of bombs in the asteroid base. Deeming him worthy to fight the Separatists, the Jedi High Council sent Vos to lead an operation to destroy a Separatist listening post on the planet Vanqor. Quinlan had been captured earlier during a mission to assassinate Count Dooku and had spent several months in Separatist captivity. As "Admiral Enigma", Vos gained an extensive knowledge about Separatist military strategy.
For this mission, Master Vos was accompanied by Master Obi-Wan Kenobi and the Jedi Knight Anakin Skywalker. Unknown to the Jedi however, Vos had embraced the dark side of the Force and become Dooku's Sith apprentice. In reality, this was merely a ruse for Vos to get Dooku to lead him to his master Darth Sidious so that he could destroy the Sith once and for all. To perpetuate the ruse that he was still loyal to Dooku, Vos leaked information about the planned operation to the Separatists. As a result, Dooku was able to evacuate the listening post before Republic forces arrived.
Expecting heavy resistance from Separatist droid fighters, Kenobi, Vos, and Skywalker flew three Eta-2 Actis-class light interceptors. They were accompanied by twenty-four ARC-170 starfighters which formed the first attack wave. As they descended into Vanqor's atmosphere and approached their target, the three Jedi were baffled to encounter no resistance. While the Jedi and the first wave approached the listening post, Kenobi ordered Admiral Block to dispatch the second attack wave because he suspected that the Separatists had set another trap.
As the Jedi starfighters approached the listening post, Vos "observed" that it had been abandoned. To be sure that this was the case, the three Jedi starfighters embarked on a strafing run in order to flush out any stragglers. While their blast destroyed the listening post's main dish and tower, their scanners were unable to detect any ships, vehicles, people, droids, or animals below. Later, the Jedi landed at the listening post where they were joined by several Clone troopers led by Clone Commander Cody. After inspecting the interior, the Jedi and clones deduced that Count Dooku had received intelligence about the operation and evacuated the facility. As a result, Kenobi and Skywalker came to rightfully suspect that there was a traitor within their ranks leaking information to the Separatists.
Following the failed Vanqor operation, the Jedi Order came to suspect that a traitor was leaking information to the Separatists. Due to Master Vos' captivity under Dooku, suspicions fell on Quinlan Vos. After meeting with Vos in private, Master Yoda was able to deduce that Quinlan had indeed fallen to the dark side. Unsure whether this meant that he had committed himself to Count Dooku, the Jedi Council assigned Vos with a mission to assassinate Dooku. If he succeeded, he would be considered innocent. But if he failed, this was enough evidence to prove that he was a traitor.
After receiving intelligence that Dooku's Providence-class Dreadnought was visiting Christophsis, Vos and his lover Asajj Ventress traveled there on her ship, the Banshee. Unknown to Vos, the Jedi had sent Kenobi and Skywalker to tail him. Using a stolen Separatist shuttle, the two Jedi managed to follow Vos aboard the dreadnought. There, they discovered Vos trying to force Dooku to lead him to his master Darth Sidious. Confronted with evidence of Vos' treason, the two Jedi promptly arrested him. However, Vos and Dooku managed to escaped, leading to a Republic assault on Christophsis.