The year is Universal Century 0133. Ten years have past since the armed resistance of the aristocratic fraction, the Crossbone Vanguard, was subdued. Tobia Aronnax is an exchange student onboard the spaceship Smashion to Jupiter, but during a surprised attack by a group of space pirates who call themselves the Crossbone Vanguard, he finds out that there were actually hidden agendas among those in the Smashion and in Jupiter itself.

After being saved by a member of the pirates named Kincaid Nau, he was taken aboard the pirate ship, the Mother Vanguard, and was convinced by its captain, Berah Ronah, to join them. The pirate group's true identity was revealed to be a guerilla group resisting the secret fraction within Jupiter, the Jupiter Empire, which intends to conquer Earth. Now Tobia must pilot one of the three powerful Crossbone Gundam to help this new Crossbone Vanguard in their quest to oppose the Jupiter Empire's plans.

In Hathaway's Flash Hathaway Noa, still haunted by his past actions (not to mention the spirt of deceased Newtype Quess Paraya), joins a terrorist organization called Mafty and adopts the false name "Mafty Navue Erin". The organization Mafty is fighting a terrorist campaign against the Earth Federation government, and they are eventually able to acquire the incredibly powerful prototype Ξ Gundam, which Hathaway becomes the pilot of. Using the Ξ Gundam Mafty attempts to attack a meeting of high-ranking Federation cabinet members in Adelaide, Australia to force them to vote down a provision which would strengthen the Federations already considerable powers.
As a point to note, this novel focuses on a version of events chronicled in creator Yoshiyuki Tomino's novelized form of Char's Counterattack, rather than his animated movie version, and as such, several discrepancies can be found between the animated work and this novel, making it more of a semi-canonical UC storyline, rather than 100% official canon.
(Source: Wikipedia)