And again...this is pretty much guessing since I've only seen the Japanese version.
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The episode begins with the same events that took place at the end of "Zoids Eve" with Van facing off with the Death Stinger, and Fiona secluding herself from Prozen.

Ryss, flying on Specula, appears in front of Prozen (Raven, Ryss, and their organoids were awakened when Fiona opened the gates to Zoids Eve). It's obvious that Ryss is no longer taking orders from the Dark Kaiser. Just when the evil man is about to give her one of his energy blasts Raven appears in the GenoBreaker. They exchange angry words, and Prozen sends three Genosaurers to attack. Ryss watches tearfully while Raven battles. Fiona sees this taking place and turns to Zoids Eve. Suddenly, stray gunfire hits the building supporting Zoids Eve causing it to activate. The Death Stinger begins to glow.

Meanwhile Lt. O'Connell is flying overhead sending aerial photographs back to the Ultrasaurus. Captain Hermann sees that the Death Stinger has regenerated once again. Also occupying the skies is Prince Rudolph and a group of Whale Kings. Rudolph sees a photo of the Dark Kaiser and recognizes him as Prozen immediately.

On the ground, Van watches as the Death Stinger's glow intensifies. In an unusual twist of fate Hiltz is transformed into a Zoid Core. He relishes his new power and burrows his way underground disappearing once again. At the same time Fiona has telepathically spoke to Van leading him to her.

Back in the square of the ancient city, Raven continues to fight valiantly, but the Genosaurers have him outnumbered. At one point gunfire shatters the glass of the GenoBreaker cutting Raven's forehead and causing blood to ooze down his cheek. (OK, gang, if I could gamble, I'd bet big bucks that the blood will be digitally erased when this airs on Cartoon Network!...Something to watch for.) Finally Raven's skill as a pilot pays off as he destroys all of the Genosaurers, but not without taking serious damage to the GenoBreaker and himself.

Van arrives in the square in time for Raven to warn him about Prozen's plan to revive the Death Saurer. Van charges at Prozen when suddenly the Death Stinger emerges from underground and strikes him down. Prozen and Hiltz exchange words, but Hiltz has become defiant. Prozen is horrified when he is slowly engulfed within a Zoid core himself. Hiltz (within his core) arises from the Death Stinger and merges with Prozen's core. Once combined the powerful core is transplanted into the most feared Zoid of all....The Death Saurer.

Everyone watches in horror as the Death Saurer comes to life. Captain Hermann informs Van that they are preparing the gravity cannon. Just as Major Shubaltz gets a lock on his target, Hiltz, in an effort to thwart their attack, fires a charged particle blast hitting the Ultrasaurus. The huge Zoid begins to tumble. Will the gravity cannon stop the deadly Zoid or will our heroes need to take drastic action? The final exciting episode will tell the tale.