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Summary of the previous part:
Young Luke Lars arrives on Devastator, just graduated from the Imperial Academy and excited about his posting: at only eighteen, he was assigned to the elite Black Squadron, Darth Vader's personal fighter squadron. He meets his wingmate Chaser, who is dismayed by finding out Luke is only a kid. However, Luke's personality and flying skills quickly endear him to Chaser, who warms up to him and introduces him to the rest of the squad. They are only few pilots, for the squadron was decimated in a surprise Rebel attack a few weeks earlier.
Soon enough, Luke gets acquainted with the reality of a pilot's life: the paperwork, the training, the perpetual lack of time. An incident with a faulty uniform tunic attracts the attention of Darth Vader on him. The dark lord is intrigued by his familiarity, his flying skills and presence in the Force.
Meanwhile the squadron's first battle is soon approaching, and Luke is nervous. He knows Biggs, his best friend on Tatooine and at the Academy, has defected to the Rebels, and he is haunted by the idea of facing him in battle.
The fight itself is tense and difficult. Held back by a powerful instinct, Luke hesitates before obeying an order Darth Vader gave him. Vader is furious, but also curious about the Force-sensitive young man that used to live near Obi-Wan's hiding place before he found and killed his old Jedi master. He decides to ground Luke and to watch him closely.
In his new functions, Luke is bored out of his mind and unnerved by Vader's surveillance. He is further disheartened to see new pilots arrive on the squadron and disquieted by the mention of "enhanced interrogation" on prisoners' files Vader gave him to sort, which calls back to forbidden Rebel meetings Biggs dragged him to despite Luke's allegiance to the Empire.
Frustrated and exhausted, Luke talks back to Vader one too many times and Vader strangles him, attempting to kill him. Luke instinctively defends himself through the Force and manages to free himself, to Vader's astonishment.
Vader talks about Luke's potential to the Emperor, who gives him permission to train him. But after Vader's abuse, Luke is reluctant to spend more time with him and turns down his offer.
Meanwhile Luke was reinstated on the squadron and progresses in his flying. After a successful battle, the squadron unites to give Luke a call sign: Shooting Star. Luke is delighted despite the call sign reminding him of Biggs, but the celebrations are cut short when Devastator is attacked.
They manage to repel the enemy, but Chaser falls under the Rebels' fire, and Luke is devastated. He asks Vader to help him improve his flying with the Force in order to better protect his squad mates. The lessons are a success: Luke progresses quickly, and Vader is happy and proud to see his talent develop. But Luke's squadmates find the way he is growing closer to Vader suspicious. A rift grows between them, for Luke cannot possibly tell them about the Force.
The gap between them only grows when Mauler, Darth Vader's wingman and their instructor, dies in battle, and Vader names Luke to take his place. Furthermore, Vader is troubled by his growing affection towards Luke and cuts his lessons short, leaving Luke alone.
However, after a meeting with the Emperor, Vader offers him lessons again; but Luke, fed up with his commanding officer's mood swings, refuses. Vader's temper flares and he orders him back into training, which Luke drags his feet to. It takes Vader much effort to finally understand his behaviour is affecting Luke negatively and to accept that he cares about him. He promises Luke he will no longer hurt him.
Meanwhile Luke is still dismayed by the lengths the Empire goes to in order to win the war: reprisals on civilians, killing of refugees. After a bloody battle, he opens his heart to Vader about it. Vader offers him apprenticeship in the ways of the Sith, and opens the possibility of a coup against the Emperor. Luke accepts.
However, the Emperor's spies have uncovered Luke's true identity and his ties with Biggs. During his visit on Devastator for Empire's Day, Palpatine accuses Luke of treason, reveals his name as being Skywalker rather than Lars and arrests him.
Luke is interrogated and put on trial. Pushed by the Emperor, a reluctant Vader tortures him to tear a confession from him, but Luke never departs from his claims of innocence. During his audience, he denounces his inhumane treatment and proclaims his loyalty to both the Empire and his father Anakin Skywalker before being sentenced to death.
Vader is reeling from the revelation and feeling betrayed by Luke's actions, especially his hiding his identity. Everything comes back to him the night before Luke's execution. Faced with the truth of his love for his son and his grief at the fate reserved to him, he understands he cannot let Luke die.
Vader frees a badly injured Luke from his cell and leads him to a ship, staring into the rising sun as Luke flies away...