In 3643 BBY, during the Cold War between the Galactic Republic and the Sith Empire, a young Jedi Knight and the Padawan Kira Carsen embarked on a mission to the heart of Justicar territory, home of the paramilitary Justicars' Brigade on the Republic capital planet of Coruscant. The Jedi's goal was to retrieve the Planet Prison, a Republic superweapon that had been stolen by the scientists on the project at the behest of their leader, Doctor Tarnis. However, the scientists were unaware that Tarnis was, in fact, a Sith Lord.
The Sith had killed the research team and stolen the Planet Prison by the time the Knight and Carsen reached the Justicars' Tower, where they had traced an earlier transmission by Tarnis. The only surviving member of the team, a fatally wounded man named Jonkan, helped the two Jedi locate the Planet Prison in the depths of the Jedi Temple. The Jedi subsequently pursued Tarnis and defeated him in a duel before deactivating the weapon and thwarting the Sith's plan to use it against the Republic capital.
In 3643 BBY, during the Cold War between the Galactic Republic and the Sith Empire, the Republic and the Jedi Order became aware that Doctor Eli Tarnis, the lead scientist on the Republic's Planet Prison superweapon project, was, in fact, a Sith Lord. Tarnis's cover was exposed when he arranged for the theft of files on the Republic superweapon initiative and allied himself with the Black Sun criminal syndicate. Tarnis contacted his research team, the members of whom were unaware of his true identity, and urged them to bring him the Planet Prison prototype, as he claimed that the Jedi were planning to shut down the project. Believing Tarnis, the five scientists secured the prototype and took it to Tarnis deep in Justicar territory, the territory of the paramilitary and Imperial-friendly Justicars' Brigade.
A young Jedi Knight and the astromech droid T7-O1 had launched a rescue mission in the territory of Black Sun after Tarnis had arranged for Black Sun to stage his kidnapping from the Senate Building, but instead of finding the scientist, the Jedi Knight learned of Tarnis's duplicity and his true identity as a Sith. Returning to the Senate Building, the Knight was sent by General Var Suthra of the Republic Military to pursue Tarnis and the stolen Planet Prison to the Justicars' Sector, where the origin of Tarnis's transmission to the Knight had been traced. The Jedi Padawan Kira Carsen accompanied the Knight in case the pair encountered the Sith Lord in their search, and the two set off for the Justicars' Sector.
With his dying breath, Jonkan aided the Knight in locating the Planet Prison.
As the two Jedi took an air taxi to the Justicars' Sector, Tarnis met with his research team in the Justicars' Tower, the Brigade's prison and interrogation center. Once he had obtained possession of the Planet Prison, Tarnis turned on them, revealing himself to be a Sith and then murdering them with Force lightning. However, one of the scientists, a man named Jonkan, was only gravely injured, and he watched as Tarnis departed with the Planet Prison prototype.
The Knight and Carsen were forced to fight their way through hostile Justicars to reach their destination, but by the time they arrived, Tarnis had already left the area, and the two Jedi found only the bodies of the research team and a dying Jonkan. Knowing he was severely wounded, Jonkan shrugged off the Jedi's reassurances that they would get help and quickly explained what had happened. In his final moments, Jonkan explained how the Knight and Carsen could track the Planet Prison: The device generated enormous amounts of heat and required time to charge to full capacity, giving them time to find and destroy the weapon before it could fire. Urging the Knight to save Coruscant, Jonkan gasped his final breath and passed away.
Using Jonkan's information, Carsen tracked the location of the Planet Prison using the room's computers. Tarnis had taken the weapon to the ruins of the Jedi Temple as a final insult to the Jedi. With no time to spare, the two Jedi raced through the Works, Coruscant's industrial and infrastructure district, toward the Temple and their final confrontation with Tarnis. The pair located Tarnis in the ruins of the Temple and defeated him in a duel, though Tarnis's death incurred the wrath of his father, Darth Angral.
The mission to the Justicar's Sector was created for Star Wars: The Old Republic, a massively multiplayer online role-playing game released by BioWare on December 20, 2011. It appears in the Jedi Knight-class story mission "Tracking Down the Traitor," in which the player pursues the Sith Lord Tarnis to the Justicars' Sector in an attempt to find the Planet Prison superweapon. While the mission does not feature any alignment choices, it is notable for being the first mission in which the player receives Kira Carsen as a companion. She serves as a guest companion for this and the next mission, which means that she cannot be sent on crew skill missions.