Star Wars Shadows of the Empire by Steve Perry

From Library Journal
Xizor, the Dark Prince and underlord of the criminal organization Black Sun, plots to kill Luke Skywalker to usurp Darth Vader's position with the Emperor. Perry is the first novelist authorized by George Lucas to reveal what happened to the familiar Star Wars characters between The Empire Strikes Back and Return of the Jedi. Highly recommended for fans of the series.
Copyright 1996 Reed Business Information, Inc.

From Booklist
Yet another prolific action-sf writer has been recruited to labor on the Star Wars series, George Lucas' stupendous mingled-media creation. The results are something of a mixed bag but, on the whole, more agreeable than not. The story takes place between the events of The Empire Strikes Back and those of Return of the Jedi, with Luke continuing his self-training as a Jedi knight and everybody else trying to track down and unfreeze Han Solo before Boba Fett delivers him to Jabba the Hutt. Unfortunately, Darth Vader is looking for his son (Luke--remember?), to turn him to the dark side of the Force, and a nonhuman criminal mastermind who makes Jabba look like a shoplifter--Prince Xizor of the Black Sun--is also after Luke, to take vengeance on Darth Vader for killing his family. We see a good deal of Vader's ambivalence toward both his son and his emperor, which led to the conclusion of Return, and Perry handles the multitudinous details of the increasingly complex Star Wars universe as competently as he deals with characters and pacing. A solid rather than an outstanding effort in the reliably popular SW canon. Roland Green