In brief, Forces of Corruption picks up where Empire at War left off, just after the events in A New Hope. As the Empire and Rebellion regroup, a new crime lord steps onto the galactic stage. Tyber Zann, a former partner of Jabba the Hutt, decides it's the right time for him and his Consortium to take advantage of the turmoil. After first settling his rivalry with Jabba the Hutt and his minions, he sets out to steal some of the Emperor's most prized possessions.
Since the designers were free from the need to stick so closely to the events of the films, they were able to come up with a very original story that lacks the familiarity of the Galactic Civil War but still feels like a natural part of that universe. Without relying on the movies to provide context for it all, the writers have put more effort into creating a plotline and cast of characters that makes sense all on its own.