Thrawn Ascendancy: Greater Good by Timothy Zahn
The adventures of young Thrawn continue in this second book of the Ascendancy Trilogy, the prequel to the canon Thrawn novel. The trilogy tells the story of Thrawn's history in his home region, the Chiss Ascendancy of the Unknown Regions, before joining the Empire.
This book takes place in the following year after Thrawn Ascendancy: Chaos Rising, putting it during the earliest days of the Empire - but with a whole new set of crises and political challenges happening unknown to those in the rest the galaxy.
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This is a book from the New Canon timeline! It's guaranteed to be consistent with future movies, TV shows, books, and comics (and almost all new stories since mid-2014).