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While G-Force is away on another important mission in deep space, Spectra takes advantage and attacks the island of Sytron on Earth. It's a small island populated only by seals, but it holds another secret. There, Spectra's forces manage to capture the entire supply of a super concentrated element called Galactite Hydronium. Sytron is the only place on Earth where this material is mined and stored. It is used to power Earth's space craft and to make sure its force fields stay together. Without it, Earth is helpless to defend against a Spectra attack.

Naturally, this is what the Spirit and Zoltar have planned. They return to Earth with a fleet of jellyfish-shaped submarines and a squad of fighter planes to hold Sytron for good. Zoltar even joins the attack in his own command ship.

G-Force is called back to Earth from their other mission and arrive to find out all but one of the Federation's sub-chasing ships have been destroyed by Spectra. They defend the last remaining ship with a deflector screen that turns Spectra's missiles back on themselves. Other Spectra forces continue their assault on Sytron. But the Phoenix can't leave the last sub-chaser and its crew undefended, so they stay there with the Phoenix stay while Keyop goes off alone to Sytron to rescue a group of miners that have been trapped there.

Keyop makes it to Sytron and comes up with a plan to rescue the miners. Keyop contacts Mark, and Mark tells him to hurry and get everyone out... they've intercepted telecoms from Zoltar who intends on wiping Sytron off the map! Keyop enlists the help of the seals on Sytron. They allow the miners to swim underneath them to escape the island. They make their way safely to the sub-chaser, with the Phoenix still flying support above. Keyop rejoins the Phoenix along with a little seal pup who has befriended him.

Using their laser search beams, Spectra is able to detect the sub-chaser and the Phoenix, but the Phoenix still has its repellor screen activated. Zoltar orders his submarines to attack, thinking the repellor screen can't be used underwater and he's correct. The Phoenix has to shut the screen down to go under and destroy the subs. By the time they resurface, Zoltar is hovering over the sub-chaser threatening to destroy it unless G-Force surrenders. They have no other choice, so they exit the Phoenix resigned to defeat. As they're listening to Zoltar's boasting, Keyop and his little seal friend jump from the Phoenix into the water, which distracts everyone just long enough for G-Force to grab their weapons and take on Zoltar and his men one-on-one!

Zoltar sees his forces losing the battle so he leaps into an escape craft and orders his aircraft to destroy the Spectra command ship! G-Force has nowhere else to run, so they jump into the Spectra command ship to try to escape or fight back. Tiny has problems with the controls, but he finally finds the main offensive weapon and they're able to use the ship's destructive ray beams to destroy the Spectra aircraft. With his fleet destroyed, Zoltar makes a quick retreat, leaving G-Force and his command ship behind. G-Force escorts the sub-chaser back, but they've also managed to save the miners and capture a Spectra ship intact!

The island of Sytron is also called Project Zulu, and because of its Galactite Hydronium mines, it is one of the most important places on Earth

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