Jedi Apprentice: The Dark Rival

The Rising Force is the second in a series of young reader novels that chronicle the adventures of Qui-Gon Jinn and Obi-Wan Kenobi prior to Star Wars Episode I: The Phantom Menace.

Publisher's Summary
Qui-Gon Jinn's past is not at rest. How can he forge of a bond with young Obi-Wank Kenobi while he is haunted by the betrayal of his first apprentice Xanatos? Xanatos was also a promising student... until the dark side of the Force intervened. Qui-Gon thought he was gone forever.

But now Xanatos is back.

And he wants revenge.