Comic Book series
Published January, March thru May 2008 as Knights of the Old Republic #25, 26, 27 & 28 by Dark Horse Comics:

Issue #25Issue #26

Issue #27Issue #28

This story is collected in:

Vector - Volume 1
(aka Knights of the Old Republic - Volume 5)

and

Knights of the Old Republic: Volume 2

and

The Old Republic: Volume 2

e-Comic Book Series
Issues #25 thru #28 published 2011
by Dark Horse Digital.

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Synopsis:
When a terrible vision reaching more than four thousand years into the future alerts the secret Jedi Covenant to the importance of Taris, they activate an operative already on this planet overrun by Mandalorians. There, in the deadly Undercity, Celeste Morne encounters a monstrous threat as many war refugees as well as Undercity residents have transformed into Rakghouls: hulking, mindless monsters bent on destruction. One bite from a Rakghoul and the transformation begins! Also seeking refuge from the invading Mandalorians in the Undercity are Zayne and Gryph who are desperately trying to escape a horde of Rakghouls when they bump into Celeste. Reluctantly Celeste rescues the bungling twosome from the monsters but they all end up in the deepest catacombs of the Undercity when they fall through the floor. There the trio discover a Mandalorian search party, not looking for refugees but for a lost ancient Sith artefact.
The Mandalorian search party return with their find to the ice world of Jebble, now a Mandalorian stronghold. Unbeknown to the Mandalorians they have three stow-aways: Zayne, Gryph and Celeste. En-route to Jebble Celeste tries a Jedi mind-trick on Pulsipher, the leader of the Mandalorian search party, to throw the artefact, known as the Muur Talisman, away. However, Pulsipher is drawn to it and is surprised when the talisman wraps itself round his wrist, but when his colleagues try to remove it they are killed by a mysterious power.
Arriving on Jebble, Zayne and Gryph are discovered but fortunately are believed to be part of a group of new recruits and are bundle off with the other recruits for armour and weapons. But when Zayne spots Celeste spying the Mandalorian command post, Gryph uses one of the oldest tricks to get all of them past the guards. Once inside, Celeste plans to continue searching for the Talisman. However, it is not long before they are discovered due to the clumsy actions of Gryph. Just as it appears to be all over, some of the Mandalorians suddenly transform in Rakghouls and both our trio and the unaffected Mandalorians are fighting for their lives. Celeste is mystified as to why Rakghouls are here and why the transformation was so quick. Just barely escaping the rampaging monsters, Celeste, Zayne and Gryph discover a massive staging area for the imminent invasion of Alderaan, an invasion that could see the Rakghoul plague going galactic.
It is clear that the Muur Talisman is somehow responsible for the transformation of the Mandalorian army into a new form of Rakghouls: able to use modern weapons these are Mando-Raks! Instead of invasion, the unaffected Mandalorians are now fighting a bitter struggle to hold back the rampaging Mando-Raks and amongst this chaos an unlikely friendship begins between Zayne and Celeste as they desperately try to warn the Republic of the Mando-Rak threat. Meanwhile, Gryph is rummaging for the possibility of financial gain when he inadvertently stumbles upon an old message from Lucien Draay - leader of the Jedi Covenant and Zayne's old Master - commanding Celeste to recover the Talisman and describing its power and effects. The Talisman's purpose is to turn those within its proximity into mindless thralls that could be commanded like soldiers; it has no effect on Force-sensitive's and many non-human species; and those already affected could spread further the infection. For these reasons, the Covenant believes there is a connection between the Talisman and the ancient, unexplained Rakghoul plague.
As Zayne stands guard outside the comm-dome, Celeste's only message is to her employer: Lucien Draay. He instructs Celeste to obtain the Talisman and to kill Zayne! But when Zayne enters the dome to send a message warning the rest of the Mandalorians to keep away from Jebble, her doubts of Zayne's guilt prevent her from slaying him. Leaving Celeste behind, Zayne goes in search of Gryph when he is captured by Pulsipher - holder of the Talisman and controller of the Mando-Raks. The power of the Talisman will restore Pulsipher's position in the Mandalorian hierarchy and he believes that Zayne can unlock its full potential. Instead the Talisman suddenly uncoils itself from Pulsipher's arm and while he finds himself the target of his own Mando-Rak guards, the Talisman is attracted to Zayne. Suddenly, Celeste bursts in killing the Mando-Raks and pulls the Talisman away from Zayne. It quickly attaches itself to Celeste whereupon she glimpses a vision - a vision of the future?
Nearly overwhelmed by an ancient evil run rampant, the Jedi Celeste Morne has made a choice of cosmic significance: her attempt to use the Muur Talisman to stop the spread of the Rakghoul plague has failed as the Talisman contains something else: an ancient Sith personality that strives to conquer the galaxy. Zayne quickly realises that something or someone is controlling Celeste, that she is not in full control of the Mando-Raks and that she is merely performing the wishes of someone else. However, for the time being, Zayne and Gryph share Celeste's protection from the Mando-Raks.
Gryph recites to Zayne the truth of Celeste and her working for Lucien Draay. When Zayne confronts Celeste he reminds her of her primary goal: to protect the galaxy from the Sith. But, so long as she wears the Talisman, she'll be working for the Sith. Celeste pleads with Zayne to kill her, but Zayne cannot do this. Instead he recalls a machine he'd seen and discussed by Pulsipher: Lord Dreypa's Oubliette, an isolation chamber capable of imprisoning Jedi and Sith alike. As Celeste enters the chamber, Zayne promises to take the chamber to the Sanctum of the Exalted on Odryn, the place Celeste was instructed to take the Muur Talisman. To assist Zayne's entry to the Sanctum, Celeste gives Zayne her key.
But as the chamber is sealed, the control previously held over the Mando-Raks is lost and both Zayne and Gryph are soon fighting for their lives and have to leave the chamber where it is. Zayne and Gryph are forced to run for their lives when they are rescued by their own ship, the Williwaw. As the Williwaw enters orbit, the Mandalorian relief force Zayne had previously contacted arrives. But as Zayne attempts communication with the Mandalorian fleet, he witnesses their total and complete annihilation of the planet's surface to ensure the Rakghoul plague is destroyed. Realising he has lost Celeste, Zayne promises to take down the Covenant and to clear all their names in the process.