Darth Vader orchestrated an attack in secret against an Imperial starship carrying confiscated credits to fund his private efforts to discover the whereabouts of his son Luke Skywalker. The Sith Lord is forced to take such drastic measures because he lost his ability to lead when Emperor Palpatine demoted him for failing to prevent the destruction of the first Death Star.
Darth Vader first acquires the contraband legally from a rogue underworld mob boss known as the Rodian for not falling under the Empire's heel. When the credits are in transit on an Imperial starship, Darth Vader enlists the help of archeologist Doctor Aphra to hire bounty hunters to attack the vessel under the guise that they are stealing from the Empire for themselves in 2015's Darth Vader #8 by writer Kieron Gillen, artist Salvador Larroca, colorist Edgar Delgado, and letterer Joe Caramagna.
Together, the bounty hunter team manufactures a meteor storm in the vicinity of the Imperial starship by destroying a massive space rock. This is done to cover up the ion charge they blast at the vessel to help them board undetected. The team then propels another massive space rock at the starship to rip apart the hull and jettison the credits into space for them to later collect. Doctor Aphra, however, intentionally loses the majority of the contraband for Vader so he can fund his efforts to find the rebel fighter who destroyed the first Death Star who the Sith Lord recently learned is his son Luke Skywalker.
This covert operation is much worse than the one the Sith Lord later leads after the events of The Empire Strikes Back in 2020's Star Wars: Darth Vader series. Like this undercover mission to steal credits from the Empire, Darth Vader's actions later on are motivated by Luke Skywalker, except he is seeking retribution against those who hid his son from him. The difference, however, is that Emperor Palpatine learns of his apprentice's side venture in the 2020 series and punishes him severely by damaging Vader's limbs and marooning him on Mustafar where he then sends the Sith assassin Ochi of Bestoon to kill him. It's obvious that if Palpatine learned of Vader's treachery in the 2015 series when he not only stole the Empire's contraband but attacked an Imperial cruiser in the pursuit thereof, his punishment would have been much worse than when Palpatine left him for dead on Mustafar.
Regardless, it's interesting that Palpatine's punishment for failing to protect the Death Star is much less severe than going rogue. After the Death Star's destruction, Palpatine doesn't test Vader by trying to kill him directly. He just demotes him. The reason is because Vader's failure wasn't the result of him losing his connection to the dark side of the Force, which is the case in the 2020 series. In fact, the Emperor reveals that there were others who were more to blame for the Death Star's destruction but they had all died so he could only punish Vader. Conversely, Palpatine later believes after The Empire Strikes Back that when Vader sought vengeance for those who kept Luke from him, his apprentice wasn't experiencing the necessary feelings of fear, anger and hate to unlock the true power of the Force. So Palpatine attempts to destroy Darth Vader. Emperor Palpatine doesn't like failure and will punish those who fail accordingly. But these punishments are more extreme when they're connected to the Force.