The Warrior's story starts on Korriban. The warrior must partake in the trials to become a true Sith. It is revealed that the warrior was in fact, summoned to Korriban by an influential overseer named Tremel, also the headmaster of the Sith Academy. The warrior was brought to Korriban early from the training grounds for younger initiates on the planet of Ziost, but was taken to the former months ahead of schedule because of an enormous potential sensed by previous masters.
With Tremel as this warrior's new master, the latter engaged in many rigorous trials to prove themselves worthy of becoming a true Sith, such as finding an ancient warblade, defeating a vicious beast inside the tomb of Marka Ragnos, and sitting in the judgement of three prisoners who posed a threat to the sith acolytes at the academy. The Sith Warrior, after engaging in these activities, caught the attention of a visiting Sith Lord by the name of Darth Baras, who summoned them to his chambers for inspection. Baras, being pleased of what he saw, decided to make the future Sith Lord his prospective apprentice, much to the dismay of the warrior's rival, Vemrin. The warrior was given new tasks to prove their worth to Baras, in hopes of becoming his formal apprentice. One of these tasks involved getting rid of their old master, Overseer Tremel.
Baras gave the warrior one final task: go into the tomb of Naga Sadow to find an ancient lightsaber. For this task, Baras gave his hopeful apprentice a Twi'lek slave girl with knowledge of Korriban's tombs, Vette, who helped break into the tomb of Naga Sadow and retrieve the arcane weapon. The Sith Warrior confronted Vemrin in the tomb, as he coveted the blade for himself which resulted in a duel that resulted in the death of the warrior's adversary. After returning to Baras, this warrior was made Baras' formal apprentice and tasked, along with Vette, to go by shuttle to the Imperial capital world of Dromund Kaas. The warrior obliged and met the Sith Lord in the Dark Citadel of the Sith Emperor.
The Sith Warrior was then given several missions by Baras that involved infiltrating and assassinating many important political and military figures in the empire. After helping their master interrogate a Republic spy, the sith warrior was sent into the Dark Temple to retrieve an ancient torture device that would be beneficial to the inquisition. The spy, before dying, revealed information regarding an extremely gifted Jedi padawan being trained by one of Baras' oldest adversaries. Crucial information was being held by two of Baras' spies, contacts on the worlds of Balmorra and Nar Shaddaa. With this new information, the warrior was dispatched to the planets to silence these two agents before the vital information slipped into the wrong hands.
Darth Baras discovers that a Jedi Padawan, under the guidance and protection of an old rival, Jedi Master Nomen Karr has been somehow able to discover elements of his spy network in the Republic. He sets the Sith Warrior on the task of first cleaning up the spy network, and then to seeking out and destroying the padawan.
To begin the task of cleaning up the network, Darth Baras send his new apprentice to Balmorra. On Balmorra, the Sith Warrior meets Malavai Quinn, an intelligence officer who will help with their mission. Their mission is to kill a Balmorran resistance general, Commander Rylon, who is really one of Darth Baras´s agents. The first task is taking down the general's son who is held in captivity by the resistance. The Warrior must fight the jailer and a squad of Republic troopers before they can get to the son. Then, the Sith Warrior must either wipe the son's memory or kills him.
Next, a similar cleanup is required on Nar Shaddaa. This time however, Darth Baras's burned agents have fallen under the protection of Lord Rathari, an upstart Sith Lord. The Dark Council has placed him in charge of their interests on Nar Shaddaa, so Darth Baras's apprentice must act without drawing unwanted attention.
With the primary cleanup handled, the Sith Warrior is sent on the trail of the Jedi Padawan. Intelligence has revealed that the padawan spent some time training on Tatooine. With local guidance from tracker Sharack Breev, the Sith Warriors follow the trail to Master Yonlach. Mastar Yonlach is a veteran of the Jedi Order and a great teacher. He was apparantly able to bring out a special gift of the padawan, the ability to see the true nature of a person, be it Light or Dark. The Sith Warrior chooses (with relating dark or light side points) kill Master Yonlach or not-both strike the first emotional blow to the young padawan who had bonded with the Jedi Master.
Having discovered that the padawan was originally from Alderaan the Sith Warrior is directed to the planet and ordered to seek out and destroy any roots related to the padawan. The plan is to continue striking emotional blows to draw out the padawan so that she can be eliminated. The unscrupulous Duke Kendoh had been tasked by Darth Baras to uncover the padawan's connection on Alderaan. He leads the Sith Warrior to House Organa. This brings the Sith Warrior into a confrontation with General Gesselle Organa. From her, the padawan's identify, Jaesa Willsaam, is learned as well as the whereabout of her parents.
After confronting Jaesa's parents, the padawan is finally drawn out. She secretly contacts the Sith Warrior and schedules a rendezvous in the Distant Outer Rim. The meeting, however, doesn't go as planned. Master Nomen Karr having discovered the planned meeting, instead sets a couple of Jedi in ambush. After dispatching the Jedi (again with a light/dark side of the force choices about both if to fight them at all and if to kill one or both of them), a distraught Jaesa again contacts the Sith Warrior, pleading for an end to his chase. At the same time, Master Nomen Karr contacts Darth Baras, calling him out to settle it between themselves.
Darth Baras sends the Sith Warrior in his place to Nomen Karr's hideout on Taris. Finally, the Sith Warrior removes the last emotional support Jaesa had left. Rather than destroy Jaesa, the Sith Warrior takes advantage of Jaesa's fragile state to sway her to join him. This marks be begining of a subplot to either to break Jaesa and turn her to the dark side or to recruit her-and join the Warrior if he or she is-as a Sith with secret leanings for the light side. Darth Baras upon discovering is surprised, but as a result of the turn of events bestows on the Sith Warrior the title of Lord.
After a brief break, to enjoy being given the title Sith Lord, Darth Baras sends the Sith Warrior back to Nar Shaddaa. Darth Baras's master on the Dark Council, Darth Vengean is looking for a way to break the truce between the Republic and the Empire and bring the two back into a full fledged war. A Republic general is meeting with some Empire traitors on Nar Shaddaa, and Darth Baras feels that killing the general might be the key.
Upon successfully eliminating General Karastace Gonn, Darth Baras is given the go ahead to begin Plan Zero, which involves eliminating all the top leaders of the Republic military. Darth Baras has six targets in mind. Four of the targets are on Taris. While Darth Baras tracks the location of the final two, he sends the Sith Warrior to eliminate the targets on Taris.
On Taris, you meet Moff Hurdenn, who quickly assigns Lieutenant Pierce to assisting you in your task. Lieutenant Pierce will provide intel from the Command Center while you start working on the targets. Your told these four generals make up the Republic War Trust. Your first target is General Frellka.