Star Wars: Jedi Knight: Mysteries of the Sith, an expansion pack, augments the gameplay of the first-person shooter Star Wars: Jedi Knight: Dark Forces II. The release date was February 17, 1998. A key draw for enthusiasts was the chance to control Mara Jade, a much-loved character from the Star Wars Expanded Universe. The narrative unfolds across fourteen stages, situated within the timeline of 10 ABY, which is five years following the events of the initial Jedi Knight installment. Numerous technological advancements and enhancements were incorporated into this expansion.
The New Republic outpost on Altyr V faces an assault from a pair of artificial asteroids under the command of the Imperial Remnant. Kyle Katarn commandeers a Lambda-class Shuttle from the attacking Imperials and pilots it toward one of the asteroids. Once there, he infiltrates the control center and turns the asteroid's weaponry against its counterpart. Following the destruction of the second asteroid, he sabotages the weapon's cooling mechanism, narrowly escaping before the asteroid detonates. While aboard the artificial asteroid, he uncovers intel concerning the planet Dromund Kaas, a location of significance to the Empire. He journeys to this planet to investigate, leaving Mara Jade to undertake several missions for the New Republic.
Mara's initial assignment involves negotiating with Ka'Pa the Hutt regarding the New Republic's provisions. To secure Ka'Pa's cooperation, Mara is compelled to pilfer the GCT, a device owned by Ka'Pa's rival, Takara. While searching for one of Takara's subordinates, Abron Mar, within the Katraasii Spaceport, Mara is ensnared by Mar. She is confined to a prison cell but succeeds in escaping and retreating into a network of pipes. These pipes lead to the den of a rancor, maintained by the pirate faction. Retrieving her lightsaber from behind the cage, she defeats the rancor and escapes with the device.
Subsequently, Mara is assigned to a New Republic Corvette tasked with safeguarding a Jedi Holocron. The vessel is attacked by the Lumini Pirates, a group headed by a smuggler known as Kaerobani. Mara fends off the attackers, but the Holocron is stolen. Mara conceals herself within a cargo container and boards the pirates' vessel. The ship transports her to Rathalay, where she recovers the Holocron and flees.
With Kyle's prolonged absence, Mara ventures to Dromund Kaas in search of him. The planet's dark side presence renders Mara's weaponry ineffective, save for her lightsaber. Battling through a vast swamp, she arrives at the Dark Force Temple. There, she encounters Kyle, driven to madness by the dark side. Mara and Kyle engage in multiple duels, with Mara emerging victorious each time. Kyle retreats further into the catacombs, eventually reaching the temple's throne room. Mara pursues Kyle, ultimately confronting him within the throne room. Mara then willingly deactivates her lightsaber, leaving herself vulnerable to Kyle's assault. Kyle finds himself unable to kill Mara and rejects the dark side.
Having recognized his errors, Kyle allowed his Force abilities to diminish. Abandoning the Jedi path, he resumed his mercenary occupation on behalf of the New Republic alongside his longtime associate, Jan Ors.
This expansion made significant improvements to the original Jedi Knight engine by adding aesthetic features like colored lights, new enemies, and Force powers (and, more controversially, removing the Dark/Light side dichotomy). Several under-the-hood changes were also made, the most important of which was that COG, the programming language used by Jedi Knight to create scripted in-game events and interactivity (doors, elevators, weapons, in-game cutscenes, enemy behavior, and many other things in Jedi Knight are controlled by COG scripts) was expanded with new functions and capabilities, which the Sith Engine made the most of. Moreover, while enemies in Jedi Knight would flee when disarmed, in Mysteries of the Sith they would attempt to fight with their fists. Mysteries of the Sith also introduced new multiplayer modes like the KFY ("Kill the Fool with the Ysalamiri") game, which was based on KFC, and included several new weapons. Some Force powers, such as Throw and Lightning, were also replaced.
The game includes a concealed level that enables the player to assume the role of Luke Skywalker during his visit to Bespin in Star Wars: Episode V The Empire Strikes Back. The LucasArts webpage featuring this information was cleverly hidden, with no links to the necessary files. The discovery of this page spread through word of mouth.
For some users, the "episode.jk" file was downloaded as "episode.txt"; renaming "episode.txt" to "episode.jk" fixed the issue.