When the Emperor and his notorious apprentice, Darth Vader, find themselves stranded in the middle of insurgent action on an inhospitable planet, they must rely on each other, the Force, and their own ruthlessness to prevail.
Anakin Skywalker, Jedi Knight, is just a memory. Darth Vader, newly anointed Sith Lord, is ascendant. The Emperor’s chosen apprentice has swiftly proven his loyalty to the dark side. Still, the history of the Sith Order is one of duplicity, betrayal, and acolytes violently usurping their Masters—and the truest measure of Vader’s allegiance has yet to be taken. Until now.
On Ryloth, a planet crucial to the growing Empire as a source of slave labor and the narcotic known as “spice,” an aggressive resistance movement has arisen, led by Cham Syndulla, an idealistic freedom fighter, and Isval, a vengeful former slave. But Emperor Palpatine means to control the embattled world and its precious resources—by political power or firepower—and he will be neither intimidated nor denied. Accompanied by his merciless disciple, Darth Vader, he sets out on a rare personal mission to ensure his will is done.
For Syndulla and Isval, it’s the opportunity to strike at the very heart of the ruthless dictatorship sweeping the galaxy. And for the Emperor and Darth Vader, Ryloth becomes more than just a matter of putting down an insurrection: When an ambush sends them crashing to the planet’s surface, where inhospitable terrain and an army of resistance fighters await them, they will find their relationship tested as never before. With only their lightsabers, the dark side of the Force, and each other to depend on, the two Sith must decide if the brutal bond they share will make them victorious allies or lethal adversaries.
A group of Twi’lek freedom fighters led by Cham await the arrival of allies piloting a stolen Imperial weapons freighter. The freighter arrives at the rendezvous pursued by none other than Darth Vader leading a squadron of V Wing fighters. As Cham and his lieutenant Isval watch from hiding, Vader disables the shields on the Imperial vessel, ejects into space, and boards the freighter. Unable to help, they listen to their friends die through an open com channel as Vader slaughters the entire crew.
Cham and Isval escape, and soon recieve intelligence that the Emperor and Vader will both soon be visiting their native planet Ryloth in secret aboard the Star Destroyer Perilous. Cham determines to launch a surprise attack to assassinate both Sith Lords, and blackmails Imperial Colonel Belkor Dray into providing support. Belkor has long secretly collaborated with Ryloth resistance in exchange for leverage against his rival in power, the apathetic and hedonistic Moff Delion Mors. While Belkor is reluctant, the threat of exposure forces him to give Cham the help he demands.
Before the attack, Isval secretly visits the Octagon, the center of vice on Ryloth. Isval grew up a prostitute in this shady neighborhood, and occasionally returns there to hunt and kill Imperial officers. She rescues a young Twi’lek woman named Ryinn from her poverty, establishing her in a secreted apartment with cash and resources to begin a new life. Isval then returns to the resistance to prepare for the assault.
Vader and Sidious arrive above Ryloth. Cham uses a minefield and a group of Shield Bleeders to weaken the Star Destroyer’s defenses, then launches swarms of Droid Starfighters equipped with explosive Buzz Droids to inflict more damage. Vader rushes to his starfighter and saves the ship, but Cham has an ace up his sleeve. Anticipating that the Imperials will call for any available repair crews, he sends several ships with strike teams disguised as maintenance workers to dock with the Perilous. One of these teams, led by Isval, successfully plants explosives in the Star Destroyer’s core. Despite pursuit by Vader himself, Isval manages to escape the doomed ship. Vader and the Emperor escape the Destroyer in an auxiliary shuttle along with members of the Royal Guard.
Meanwhile, Moff Mors finds herself stirred to sudden action by news of the attack. Belkor attempts to route rebel forces to intercept and destroy her ship, thus paving his way to power. At the same time, he provides the resistance with information necessary to identify the Emperor’s shuttle. As the Star Destroyer explodes nearby, rebel ships attack and disable both shuttles. Vader manages a safe crash-landing on Ryloth’s surface, and Mors is saved by the auto-piloting system.
Belkor transmits information which allows Isval’s ship to get near an Imperial communications station on Ryloth. Isval destroys the comm array, severely limiting communications on the planet’s surface and preventing Vader and the Emperor from calling for help. A group of resistance ships attack Vader and Sidious, but the two combine their power to deflect the attacks and grounds their vessels with the power of the Force. They then escape into the jungle.
Moff Mors rushes to the ruined communication station. Now sure that Belkor is a traitor, she enlists the aid of an efficient Imperial officer and old friend, Major Steen Borkas. Together they begin to search for the Emperor. Meanwhile, Cham and Isval begin searching for the downed imperials with the help of Belkor, whose mental state is deteriorating from the stress.
In the jungle, Vader and Sidious are attacked by colossal insectine predators called Lyleks. Driven by a vast hoard into a subterranean maze, they engage hundreds of the huge creatures, defeating both the drones and a gargantuan queen. Vader finds himself briefly tempted to allow his Master to die so that he might ascend to rule the Empire, but resists the urge. The two escape from the den and meet a young Twi’lek woman from a primitive tribe. Sidious moves to cut her down with his lightsaber, but Vader stops him, pointing out that the village might have a ship they can use. Sidious informs his apprentice that Vader’s mercy has doomed the entire village.
The villagers welcome Sidious and the Emperor, oblivious to their identities. Cham’s forces find Vader at almost exactly the same time as Belkor’s traitors and Mors’ rescuers. Unknown to Belkor, Moff Mors has alerted the forces under Belkor’s command to his treachery. The air strike Belkor calls in to destroy the Emperor instead blows his ship from the sky. Mors lands near the Emperor with a force of stormtroopers, driving the Twi’lek resistance away. Isval is captured by Vader, sacrificing herself to help Cham escape.
Sidious then reveals to Isval that the entire exercize was planned by him. He allowed the attack to take place so that the growing Twi’lek rebellion would burn out before it could spread to become a true threat. The incident was also a test of Darth Vader’s power and loyalty. Sidious then orders Isval killed and instructs Vader to slaughter everyone in the village so there will be no witnesses.