Thrawn: Alliances further fleshes out Thrawn’s backstory in addition to further implementing him into the main Star Wars story. The previous book dealt with Thrawn’s introduction into the Empire and rise through its ranks. Alliances touches on that by showcasing his encounter with Anakin Skywalker during the Clone Wars, mentioned in the first novel. This book flips back and forth between those flashbacks and a team-up between Thrawn and Vader occurring shortly after Star Wars: Rebels Season 3 finale. Both stories involve the same planet and hold memories for both Thrawn and Vader.
The two stories flip back and forth fairly frequently throughout the novel. In the Clone Wars era story, Padme goes missing and Anakin sets out with R2D2 to find her. Along the way, he encounters Thrawn, on a mission for his own people and willing to work with Anakin to achieve both their goals. This was one of the darker, Rogue One-esque, stories that Disney has written into their continuity. The implications of the plot Padme stumbles upon are obvious to anyone who knows how the Clone Wars end. But the real horror comes from seeing how often and how tragically civilians were caught in the crossfire.
The more modern story involves Thrawn and Vader investigating a disturbance in the Force felt by Emperor Palpatine. The most interesting parts of these bits were the parts from Darth Vader’s point-of-view. With the past-present story swapping, it was very interesting to see Anakin Skywalker and Darth Vader in the same story. The flashback story takes place near the end of the war, so readers see Anakin’s anger the ultimately creates Vader. Vader in a book is very different from Vader in the films since his emotions are easy to see. Sections of the book from his point of view display him as clearly angry even though other characters can only see his faceless mask.
On the whole, Thrawn: Alliances does more for Vader as a character than Thrawn. Throughout the book, Thrawn continues to be a patient, almost impassive, but extremely efficient military officer. He is more integrated into Imperial society, no longer the newcomer he was in the first book, and better at playing politics. Even with someone as unforgiving and dangerous as Darth Vader for an opponent. Despite both being high-ranking Imperial characters, Vader and Thrawn’s personalities and command styles clash immensely. Seeing them put as a pair was interesting and some of the world building here opens the Star Wars universe up to many more future adventures involving the Chiss.