Heir to the Empire is the first book in a trilogy of novels known as Star Wars: The Thrawn Trilogy, all written by Timothy Zhan.
Heir to the Empire is part of the Star Wars Legends, and takes place five years after the events of Return of the Jedi. The Rebel Alliance has destroyed the Death Star, defeated Darth Vader and Emperor Palpatine, and driven out the remnants of the old Imperial Starfleet to a distant corner of the galaxy. Princess Leia and Han Solo are married and expecting twins. Luke Skywalker has become the first in a long-awaited new line of Jedi Knights.
Thousands of light years away, Grand Admiral Thrawn, the last of the Emperor's Warlords, has taken command of the shattered Imperial Fleet, readied it for war, and pointed it at the fragile heart of the New Republic. Thrawn is searching for a Dark Jedi and is succeeding in restoring the Empire. More: en.wikipedia.org.