BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
Jacen Solo is one of the most well-developed characters in the Legends timeline. His experiences in the hands of Vergere and the Yuuzahn Vong changed him irrevocably. He saved the galaxy once, but to what lengths is he willing to go in order to save it again? Betrayal takes his story in a new direction, reintroducing a villain from the original Marvel comics, Lumiya, who guides Jacen along a dark path. All the while, Jacen is serving as the Jedi teacher to his nephew, Ben Skywalker, and the Skywalker and Solo clans might be torn apart along family lines.
It would be helpful to have read the New Jedi Order before starting Legacy of the Force, but we realize that's a tall order. At the very least, you'll want to familiarize yourself with the main characters and with Jacen's torture at the hands of Vergere in Traitor before diving in.
This is the era of Luke Skywalker's legacy; the Jedi Master has unified the order into a cohesive group of powerful Jedi Knights. But as the new era begins, planetary interests threaten to disrupt this time of relative peace, and Luke is plagued with visions of an approaching darkness. Evil is rising again—out of the best intentions—and it looks as if the legacy of the Skywalkers may come full circle. Honor and duty will collide with friendship and blood ties as the Skywalker and Solo clans find themselves on opposing sides of an explosive conflict with potentially devastating repercussions for both families, for the Jedi order and for the entire galaxy.
When a mission to uncover an illegal missile factory on the planet Adumar ends in a violent ambush—from which Jedi Knight Jacen Solo and his protégé and cousin, Ben Skywalker, narrowly escape with their lives—it's the most alarming evidence yet that sparks of political unrest are threatening to ignite into total rebellion. The governments of numerous worlds are chafing under the strict regulations of the Galactic Alliance, and diplomatic efforts to enforce compliance are failing. Fearing the worst, the Alliance readies a preemptive display of military might in a bid to bring the rogue worlds to heel before an uprising erupts. The designated target of this exercise: planet Corellia—renowned for the brash independence and renegade spirit that have made its favorite son, Han Solo, a legend.
Something of a rogue himself, Jacen is nevertheless duty bound as a Jedi to stand with his uncle, Jedi Master Luke Skywalker, on the side of the Galactic Alliance. But when the wary Corellians launch a counterstrike, the Alliance's show of force—and a secret mission to disable Corellia's crucial Centerpoint Station—give way to an armed skirmish. Once the smoke clears, the battle lines are drawn. Now the specter of full scale war looms between a growing cadre of defiant planets and the Galactic Alliance that some fear is becoming a new Empire. And even as both sides struggle to find a diplomatic solution mysterious acts of treachery and sabotage threaten peace efforts at every turn.
Determined to root out those behind the mayhem, Jacen follows a trail of cryptic clues to a dark rendezvous with the most shocking of revelations—while Luke grapples with something even more troubling: dream visions of a shadowy figure whose Force power and ruthlessness remind him of Darth Vader—a lethal enemy who strikes like a dark spirit on a mission of doom. An agent of evil who, if Luke's visions come to pass, will bring untold pain to the Jedi Master—and to the entire galaxy.