Jack and Arcee walk through Kaon, guided by the light of the Key to Vector Sigma. They come upon a circular clearing, and the key glows intensely, indicating that they must be close. Suddenly, the ground begins to shake, and cracks appear in the surface. The duo watch in awe as a passageway rises from the ground, its door illuminated the same as the Key. It opens, but just as the two are about to enter, an enormous insect-like creature rears up from atop the passage.
Arcee's Autobot symbol catches its eye and it charges her. But Arcee, being speedy and agile, but not very strong was not able to injure it. She is quickly incapacitated, and the creature notices Jack, giving temporary pursuit until distracted by Arcee. Jack radios Ratchet and is told that the creature is an Insecticon, one of many sentries left to guard the dead Cybertron. Arcee tells Jack to go, to his surprise, but he realizes the necessity. As he enters, the door closes behind him.
On the Nemesis, Megatron inquires as to Orion's progress on Project Iacon. Orion says it's tough work, but Megatron says otherwise, revealing to him that all of his unsanctioned research has been recorded. Orion takes the opportunity to ask about his reported affiliation with the Autobots, but Megatron merely tells him to get back to work. Orion decides that enough is enough, and erases his progress in the archives. Megatron laughs, and shows the clerk that he has been recorded and documented in his pursuits. Soundwave intrudes, to show Megatron that one of their sentries came online on Cybertron. Orion asks how anything is alive on the planet, but Megatron tells him to continue his work-or be terminated.
Back on Cybertron, Arcee tangles with the enormous bug, but is no match for its brute strength. Finished with her, the Insecticon turns its attention to the fleshling, and breaks its way into the tunnel.
In the depths of the tunnel, Jack hears a familiar noise, and uproots a metal bar for protection.
Back on the Nemesis, Megatron reviews the reports with Soundwave. He learns of the Space Bridge's activation, its endpoint, and the fact that it is still active. He quickly deduces the Autobots' plan.
In Cybertron's depths, Jack arrives at the chamber of Vector Sigma. He proceeds to the center of a circular platform, where he places the Key. The entire chamber begins to transform and glow with the Key's energy, and the enormous supercomputer reveals itself, and begins to transfer its energy to the Key.
On the Nemesis, Orion is hassled by the guards. He appeals to their "good nature," saying that he believes Megatron will use the information he is agglomerating for nefarious purposes. Good-old fashioned police brutality ensues as the helpless clerk is kicked and punched by his guards.
In the chamber, Jack is antsy about the speed of his download. His problems lie beyond his dial-up however, because behind him, a horde of Scraplets has just woken up. While they have no interest in harming Jack, they quickly notice the very alive metal before him, in the form of Vector Sigma (a spinning ball of blue light) and the Key. Jack is helpless to fend them off, and they begin to snack on the delicious download port. He reports frantically on his position to ground control.
In the Space Bridge chamber, however, the Autobots have problems of their own as Megatron steps out of a Ground Bridge to them. Ratchet tells them that they must hold the Bridge at any cost, and the battle begins. Unsurprisingly, Megatron easily floors every Autobot twice.
On Cybertron, Arcee awakes to find a Scraplet chewing on her foot. She blasts it off, and notices the opened passage — and the absent Insecticon. Transforming, she speeds into the passageway.
Jack valiantly smashes the Scraplets as they feed, but is unable to stop their progress towards the Matrix. Another problem presents itself behind him in the form of the Insecticon. It charges towards him, but stops in its tracks, staring at the Key. Jack realizes why, and the Scraplets suddenly become a blessing. He formulates an idea, pulling a Scraplet off the Key and pointing it at the aggressor. The Insecticon turns tail as it realizes what's happening, but the Scraplets give chase and latch on, quickly chewing through the giant insect as it falls to its doom, limbs disconnected. The download completes, and Jack retrieves the key. Arcee finally arrives, and the two depart.
The Vehicon guards continue to beat down Orion, and one of them lets slip that it's a privilege to beat the former leader of the Autobots. Orion pleads with them to stop, and in desperation, he accidentally activates his blasters. He is shocked to realise that he has been installed with any weapons, and the guards realise they are in trouble, firing upon him. He is further surprised by the ease with which he dispatches them.
Arcee and Jack arrive at the Space Bridge portal, and radio Ratchet about their position. Total silence on the comm tip them off that something is wrong, and, undetected on the other end of the portal, Megatron waits to end the lineage of the Primes. However, he is surprised by the sudden arrival of Orion Pax, who vows that, no matter what his heritage might be, his spark sympathises with the Autobots. He deploys his blades, and charges for Megatron, but is quickly defeated. Megatron says that he has much to learn, and prepares to kill him, but Arcee speeds through the bridge and collides with him, sending them both flying. In the light of the bridge, Jack presents the Key to Orion, who hesitates in his humility, but accepts his destiny.
The Key begins to upload the Matrix to its host. Megatron, preoccupied with fighting Arcee, notices this, and desperately runs at him. However, Orion Pax—now Optimus Prime once again—isn't ready to go down again, and trounces his enemy. A Ground Bridge portal opens up, and the Autobots retreat.
At base, the Autobots and humans rejoice at their reunion. Noticing his Decepticon symbol, Optimus asks Ratchet what had happened. He replies that it was their darkest hour, but at every point along the way, Optimus was truly an Autobot inside his spark.
- Ratchet: An Insecticon!
- June Darby: A what?
- Raf: What are Decepticons are doing on Cybertron?
- Ratchet: A few remained in stasis... sentries should the enemy return?
- June Darby: Listen up, Jack. Optimus is counting on you.
- Jack Darby: Roger that, Mom.
- Optimus Prime: Why does history portray me siding with the Autobot aggressors? And why did Starscream call me a Prime? I'm must know! Who am I?
- Megatron: One of our sentries are activated on Cybertron?
- Optimus Prime: You told me our planet was dead?
- Optimus Prime: Please we can warn them.
- Ratchet: What is it, Jack?
- 'Arcee: Ratchet, we got the Matrix. Ratchet? Somethings wrong.
- Optimus Prime: I can't let that happen, Megatron.
- Jack Darby: You have no idea.
- Optimus Prime: Megatron, be gone!
- Optimus Prime: Ratchet, how did we arrive from here?'
- Arcee: It's ours!
- Optimus Prime: Autobots, fall back!
- As Megatron notices Jack recharging Optimus's Matrix and lets go of Arcee, his shoulder armour goes through the wall.
- Before the restored Optimus jumps trough the Ground Bridge while firing at Megatron, his right shoulder can be (very briefly) seen bearing the Autobot symbol, but it should still be Decepticon.
- In the episode "Shadowzone", when the two Ground Bridge portals opened in close proximity to each other, the energy from both fed back on each other (as stated by Ratchet), and there was an explosion. Here, the Autobots' Ground Bridge portal opened right next to the still open Space Bridge, yet nothing happened
- June takes an extremely long hiatus after this episode, not returning until Darkest Hour, 23 episodes after this.
- Look closely at the arena in Kaon: it's the same arena as seen in "One Shall Rise, Part 3". Ironic that the entrance to Vector Sigma lay beneath Megatron's feet at that moment.
- When the Scraplets look at Vector Sigma, most of the room is boring old dead metal, but the spinning blue light comes up in their vision as living metal. The download area is clearly even more delicious.
- When Jack coaxes the Scraplets into attacking the Insecticon, he calls it "the main course", echoing what Bulkhead said while using himself as bait in "Scrapheap".
- The way Optimus catches Megatron's sword just after he regains his memory is exactly the same as when Megatron caught Optimus' sword in "One Shall Fall". It even makes the same thundering noise.
- Jack never picked up a souvenir for Raf, which Raf asked for in the previous episode. No one ever brings souvenirs for Raf.
- You'd think that despite knowing that Orion was not as good a warrior as Optimus, Megatron would have ordered that he be disarmed.
- This is the last live appearance of the Scraplets (they'd later appear in a flashback during "Toxicity").
- The scraplets seem a lot nastier in this episode, chewing so fast as to render a hulking robot limbless in a matter of seconds. This is not an error, as many factors could contribute, such as the scraplets' inability to find living metal on the barren Cybertron and the ancient state of the Insecticon.
- Optimus still has the broken sword from way back in "One Shall Fall". It would seem that the Decepticons neglected to repair it. Or rather, neglected to mention that he had weapons in the first place.
- Adaptations of this episode include a screen-capture-style comic version as part of The Orion Pax Saga.
- Megatron says that he won't underestimate the autobots again.
- This is the third time Optimus and Megatron battle.
Main Article: Orion Pax, Part 3 Gallery
Orion Pax, Part 3}}