Star Wars: Purge - The Hidden Blade

In Darth Vader (2017) #7, Darth Vader is tasked with bringing Jocastu Nu to the Emperor alive.  In Darth Vader (2017) #10, Darth Vader is successful in capturing Jocasta and recovers a memory crystal from her that contains the names and locations of force-sensitive children.  Jocasta explains to Vader that Palpatine wants her alive because of that list and wants more Dark side disciples like Vader.  Vader, troubled by this, kills Jocasta and destroys the memory crystal.  He lies to the Emperor, telling him she died trying to escape and he did not learn anything from her.

The idea of Darth Vader disobeying the Emperor was also explored in the Expanded Universe.  One such example is in the one-shot, Purge - The Hidden Blade.  The Empire's Tremor Base is dedicated to the construction of AT-AT Walkers on the planet Otavon XII.  The native Otavi are fighting the Imperial occupation of their planet, disrupting the work, and Darth Vader is sent to hasten the construction.  Vader has been repelling Otavi attacks on the base, allowing General Crik to concentrate on the work.  Vader is clearly frustrated by the assignment, feeling it is beneath him.

Darth Vader: I've lost contact with the squad searching for the Ovani's leader --
Emperor: You were sent to hasten construction of the Walkers, not pursue the natives.
Darth Vader: Both seem a poor use of my training.
Emperor: You forget your place, Lord Vader.  Your obsession with the Jedi has clouded your judgment.
Darth Vader: I do sense a powerful presence here, my Master.  I am sure of it.
Emperor: You will remain at Tremor Base until the Walkers are complete.  If you defy my orders again, you may never leave.
Darth Vader: As you wish, my Master.

When a wounded troop from the squad returns to the base and informs Vader that there is a Jedi with the Otavi, Darth Vader sets out to kill the Jedi.  Vader finds the Jedi's Padawan first who reveals where the Jedi is prior to Vader killing him.  Next, he is attacked by Otavi who deploy a subsonic frequency sound emitter that calls a large creature, a Sugati, that attacks Vader.  Vader is able to control the creature's mind and uses the creature to travel further from the base to where the Jedi is.  The Sugati is lured away by another sound emitter while Vader attacks the Jedi, slicing the Jedi's lightsaber in two.  The Jedi surprises Vader when he pulls out another blade and attacks Vader, causing Vader to drop his lightsaber.  Vader reveals he has the Padawan's lightsaber and fatally thrusts it into the Jedi's abdomen.  These are the overt references to the title of the story, hidden blades, but another more subtle reference is revealed when Vader returns to the base to see it was overrun by the Otavi with the help of the monstrous Sugati.  As Vader is overlooking the destruction, the Emperor flanked by his Royal Guard appears and tells Vader to "meditate on your failure here" and leaves on his shuttle.  The Jedi had used another hidden blade successfully, the Otavi attack on the base, while Vader was distracted in his pursuit of him.

Star Wars: Purge - The Hidden Blade a - Dark Horse Comics, U.S. (April 2010)
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Star Wars: Purge - The Hidden Blade b - Dark Horse Comics, U.S. (April 2010)
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This story shows just how obsessed Darth Vader is with hunting down and killing the remaining Jedi.  He was willing to defy the Emperor, even when it results in a defeat for the Empire, in his pursuit of the Jedi.