Transformers: Prime/Recap/S1/E23 One Shall Fall

Optimus Prime recites a passage from the Covenant of Primus, foretelling that a perpetual conflict will culminate when the forty-seven spheres align. Despite the other Autobots' lack of faith, Ratchet realizes that the "world forged of chaos" referred to in the prophecy is Earth—and that the alignment will occur in a matter of days.

Aboard the Nemesis, Megatron explains to Knock Out that he sought the blood of Unicron so that he could conquer worlds with undead armies. Knock Out assures him that more Dark Energon awaits amongst the stars, but advises him not to push himself, since he was in stasis. Megatron then claims that he is the "rising darkness" of which the prophecy speaks.

Jack, Raf, and Miko find a picture of Bumblebee while searching a conspiracy website. Raf replaces the image with a dancing cat, which makes Ratchet laugh. Jack then invites Optimus to take a look, but is flatly denied. Ratchet then states that, before he became a Prime, Optimus behaved quite similarly to Jack. Agent Fowler suddenly interrupts and reveals that the Decepticons have been stealing components to build a second space bridge. Back aboard the Nemesis, Knock Out and Soundwave inform Megatron that the only item left on the list is an ample power source, which can be found in a heavily fortified human base. Airachnid could simply tunnel in, but Megatron rather angrily declares that the time for stealth is over, and he sends a massive squad of Vehicons to retrieve it. Optimus warns Fowler to have his troops evacuate, for fear of human casualties.

Optimus, Bulkhead, and Arcee arrive to fend off the Vehicons, and all goes well until Megatron himself heads out toward the battlefield. En route, he spots Bumblebee, who was taking Raf racing. Megatron opens fire, frying Bumblebee's systems and knocking Raf out cold. Megatron arrives at the base just as the Autobots disable the last of his drones, and he taunts Optimus as Bumblebee arrives whilst carrying a wounded Raf. Bulkhead restrains the enraged scout before Optimus orders Arcee to take him and Raf back to base. Megatron then ascends onto the Nemesis with the power source. Unbeknownst to Megatron, Optimus and Bulkhead climb aboard the Nemesis's hull.

Back at Autobot Outpost Omega One, Ratchet panics that his tools are wrong for human examination, and Jack suggests that they call in his mother. Meanwhile, Megatron has another vision in which he sees a sinister face and a volcano. He then orders Knock Out and Airachnid to complete the space bridge, as there is something he must attend to. June arrives at the Autobot base and quickly unnerves Ratchet with the knowledge that Raf will die unless she can stabilize him immediately. Bumblebee vents his frustration on a nearby wall, but Arcee manages to calm him...a little. Ratchet regrets having not bothered to learn human science and medicine, despite accepting the children into their lives. He then states that he has grown to need Rafael, just as Raf needs him.

Bulkhead and Optimus storm the Nemesis, and Optimus claims to have had a change of heart: He orders Bulkhead back to base with the power source, declaring that there is something he must do. He then muses grimly that he has realized that Autobots and Decepticons will never co-exist peacefully, and he vows to destroy Megatron.

As the planetary alignment nears, Megatron arrives at the volcano site, and Optimus uses a Vehicon comm link to challenge him. Optimus soon joins him at the base of the volcano, and the two exchange brief banter before engaging each other in fierce battle.

Meanwhile, Ratchet realizes that Raf has been infected with Dark Energon and theorizes that exposure to normal energon should cure him. He takes a sample from Bumblebee, placing Raf in a sealed chamber to test his theory as the others watch helplessly. Rafael soon opens his eyes, his pulse stabilizing.

Optimus appears to defeat Megatron and prepares to deal the final blow, but the Decepticon leader catches his sword with unusual strength as the volcano begins to erupt. Strange purple markings glow to life across his body, and he quickly overpowers Optimus. He realizes that the volcano is spewing forth Dark Energon, and he moves to kill Optimus, as he saw himself doing in a previous vision.

To be continued...

Tropes
"whilst fighting Megatron: Your defeat was foreseen here by the ancients. What was it they wrote? 'The weak shall perish'? Optimus: Do not believe everything you read."
 * Barehanded Blade Block: Pulled off by Megatron against Optimus.
 * Berserk Button: Megatron hurting Raf triggered the Autobot's anger, particularly Bumblebee and Optimus.
 * Blood From the Mouth: In his Unstoppable Rage, Optimus punches Megatron hard enough across the face. Repeatedly.
 * Car Fu: Performed by Optimus by grinding his tires into Megatron's face.
 * Casual Danger Dialog:

"Megatron: How was it that you put it, Optimus? "I could not have allowed this to end otherwise"?"
 * Eye Scream: Megatron gets this when Optimus knocks him off a cliff, lands on him and starts to grind his tires into Megatron's face.
 * Ironic Echo:

"Megatron: It seems I swatted a bee and squashed a bug."
 * Kick the Dog:

"Jack: Hey Optimus! Want to see something funny? Optimus: No."
 * No-Holds-Barred Beatdown: Optimus towards Megatron.
 * No Sense of Humor:

"Optimus: Megatron must be destroyed."
 * Papa Wolf: Injuring Raf is a sure way to trigger Optimus's Unstoppable Rage.
 * Tranquil Fury: Optimus retains composure even while saying...
 * Wham! Line: