A voice-over from Yoda explains that the planet Mon Calamari has split between its two native species: the Mon Calamari who are loyal to the Galactic Republic, and the Quarren, who have joined the Confederacy of Independent Systems. The Quarren have formed a Separatist-aligned government, the Quarren Isolation League, and taken over the planet.
The voice-over is revealed to be a hologram of Yoda communicating to Jedi Master Kit Fisto on the bridge of his Acclamator-class assault ship. Yoda orders Fisto to help the Calamari to retake the planet in the name of the Republic.
The Acclamator fleet carrying Fisto’s army “lands” on Mon Calamari, floating on top of the world-spanning sea. The aquatic Fisto leaps first into the water, with several divisions of Kit Fisto’s SCUBA troopers following behind him.
The Battle of Mon Calamari begins when the Republic forces come under attack by Manta droid subfighters, Sub Carriers and Mini-subs, as well as Quarren and battle droid soldiers. The Republic army is reinforced by the Mon Calamari Knights.
The trouble begins for Kit when the Quarren unveil their Crab cannon, using it to destroy several of his floating Acclamators. With the help of the Knights, as well as a use of the Force, the Cannon is first critically damaged, then pushed off the edge of a steep underwater ravine. The tide of the battle then turns in favor of the Republic.