In the previous part, Sonic and Tails joined the robot resistance in a ruined Morristown to deal with a surface bot responsible for a robot uprising. The bot in question turned out to be Tails' old creation, Hypno-bot, now sentient and capable of speech; he'd turned evil and plotted to destroy all organics as a result of Tails unintentionally abandoning him. On the ground, Knuckles, Amy, and Sticks ultimately managed to inspire the villagers to lend them a hand in holding off the robots attacking Hedgehog Village long enough for Hypno-bot to be defeated. But it wasn't all good news— Sonic's leg was hurt because Tails was unable to take a shot at Hypno-bot, and Tails feels bad about that and unknowingly causing the robot takeover in the first place. Unfortunately, Eggman found Hypno-bot in the frozen lake he plummeted into and has plans for him...
But first, back to the lead-lined bunker within Morristown, where Mighton tells Sonic and Tails what an honor it was to fight by their side as they saved the world and offers them a tour through the city. Sonic insists they need to return home... at which point Amy calls him on his Communicator and asks him when he's getting back. At this point, even Mighton and Bolts can assume the two are in a relationship, which Sonic denies. Changing his mind, he tells Amy that he and Tails are gonna stay in Morristown for a little while longer and "hang with [his] bros", then ends the call before she can finish her sentence: "Don't forget we have that—" Needless to say, Mighton and Bolts only seem further convinced. Maybe Sonic shouldn't have his Communicator on speakerphone next time.
At Eggman's lair, however, trouble is brewing. The evil scientist is ordering Orbot and Cubot to carefully chip away at the ice around the still-frozen Hypno-bot. Eventually, the ice shatters, and Hypno-bot is freed, only requiring a jump-start to his battery from Eggman to come back online. The robot's not fond of waking up next to an organic, however, and he orders Orbot and Cubot to protect him, but his barely-working hypno-ray fails to hypnotize them. Eggman attempts to convince Hypno-bot that he knows him, informing him of the time he took him over and used him for evil; Orbot, not seeing that as the best thing to say, suggests a different approach, and Eggman backpedals and says he saved him from the icy lake (Orbot approves). Hypno-bot seems to appreciate the fact that Eggman didn't leave him behind like "that turncoat, Tails". In response, Eggman says he hates the fox, too, and they also share a hatred of Sonic. Obviously, the two hit it off and become BFFs— evil BFFs.
Later, Eggman has repaired Hypno-bot and given him a little extra: an unfoldable neck-mounted gun. This apparently prompts Hypno-bot to believe that Eggman's more than just a filthy meatbag, and he proposes an alliance so they can rule Morristown together and get Sonic and Tails (and presumably the rest of Team Sonic) off their backs for good. Eggman agrees to this, and Orbot and Cubot are ecstatic that they finally get to go to Morristown, but Eggy insists they have more important business to tend to in the lair... namely, making sure his DVR records his shows. Hypno-bot, back at full power, once again hypnotizes all robots around him, and they and the evil duo fly towards Morristown. The mass of robots flying through the sky is easily noticed by Knuckles, Amy, and Sticks in the Village Center as they clean up the remnants of the robot invasion, aided by FriendBot. Amy says Sonic and Tails are definitely gonna need their help with that many robots, and as FriendBot is hypnotized, they leap onto him, using him as a ride as he joins the cloud of mechanized madness headed for Morristown.
Unaware of the looming threat, Sonic and Tails are being shown around the now-repaired Morristown by Mighton and Bolts, with Tails taking pictures of the incredibly similar buildings in the city (that's by choice, mind you). But unfortunately for them, the peace and quiet is about to come to a screeching halt, as there's a loud pounding on Morristown's glass dome. It's Eggman's Mega Bot, slamming down on, then finally crashing through the dome, allowing Eggman and his horde to enter. But he's not alone; Hypno-bot is back to finish what he started, and with Eggman's enhancements, he's certain he'll win this time. Eggman orders his robots to attack... and they do nothing, so he sheepishly asks Hypno-bot to help him out.
As the robots converge on the heroes, Sonic is confident that they can take 'em— that is, until Cowbot shows up with reinforcements. Fortunately, the heroes have reinforcements of their own: Knuckles, Amy, and Sticks arrive riding FriendBot, and Team Sonic is reunited (and it feels so good). Now a fighting group of seven, the heroes easily tear through the mechanical army of evil (with Sonic and Amy sharing some banter that's definitely not coming off as lovey-dovey at all, nope). Mighton becomes especially miffed when Cowbot attacks his pal Bolts, shooting his fists into Cowbot's mouth and destroying him from the inside. But Hypno-bot ain't letting them off that easily; he re-hypnotizes some of Morristown's citizens... and adds Mighton to his ranks. Gulp.
Outnumbered and outmatched, Sonic has no choice but to order Tails to take the other Team Sonic members and retreat. He then hoofs it to Bolts, picks him up, and runs as fast as his leg-and-a-half will take him so Hypno-bot's signal doesn't affect the diminutive robot, too. Bolts points Sonic to the location of the lead-lined bunker, and he takes him there. Meanwhile, the other Team Sonic members are running from the robot horde and manage to hide in a corridor which, luckily, is the very same dead end containing the bunker, and Sonic alerts them to it; soon, they all slide down into the bunker. Reviewing the facts, Knuckles somehow thinks everything went fine, but Sticks brings him back down to earth, knowing it was a total disaster (and compliments Bolts on the bunker). Bolts further underlines the reality of their situation, saying that if he managed to get the other robots down here and reprogram them, they'd just get re-infected once they left the lead-lined walls (another thing Sticks applauds him for). And Tails only hammers it in by saying that while Hypno-bot doesn't affect organic beings, the five of them just aren't enough this time.
But that last statement sparks an idea in Bolts' head, which he's quick to voice: what if he could just make more of Team Sonic by collecting their DNA to create cyborg copies of them? Tails adds that if they have organic brains, there's no way for Hypno-bot to take them over. The team is quickly down for this... with the obvious exception of Sticks, who's already not happy she's been pulled into a robot civil war and definitely doesn't want a robot messing with her DNA to create a cyborg duplicate of herself. Amy manages to bring her in by saying the robo-apocalypse will win if she refuses, though; she can't say "no" to that. And so, after a long period of gathering the team's DNA and working on their project, Tails and Bolts eventually get things done, and Bolts introduces Team Sonic to their new cyborg doubles, dubbed Team Cybonic (and Amy notes he hasn't gotten any better at naming things). Each of the cyborgs are the spitting image of their counterpart, only with metal in place of flesh and cloth alongside glowing, light-blue eyes (also, Knuckles' cyborg double wears a bolo tie, as requested by Knuckles himself so he could see how he'd look with one). Sticks still doesn't trust the cyborg copy of herself, and funnily enough, said copy agrees with her, considering the whole idea to be nuts. Yep, that's Sticks' DNA, alright.
Outside the trapdoor, Eggman has gathered a small portion of the robot army, ordering them to blast Team Sonic to bits as soon as they exit. But they don't. Team Cybonic does. Their field test goes wonderfully— they effortlessly tear through the robots and head outside, and Hypno-bot definitely notices and tries to hypnotize them. No dice, says Cyborg Sonic; he then tells everyone that Hypno-bot is their main target. First things first, though— they need to smash his robot goons to even touch him. But come on— we all know Team Sonic didn't get this far to back down now. The final battle begins as they charge at the enemy robots, each Team Sonic member working in perfect tandem with their cyborg double to decimate the army, minion by minion, big or small (not destroying the robots that the heroes are friendly with, of course), in a beautiful display. Sticks even starts to take a liking to Cyborg Sticks, as they think exactly alike (probably because they have the same brain).
Thanks to the heroes' increased numbers and synergy, the robot army is soon whittled away to almost nothing. Sonic takes initiative, running towards Hypno-bot to finish the fight once and for all... or so he thinks. After all, there's one little wrinkle he forgot about: the hypnotized Mighton. A surprise rocket punch from the robot hits Sonic in the side. He slides across the ground as he screams in agony and clutches his injured leg, unable to move or even get up because the pain was brought rushing back from the impact. Hypno-bot seizes the opportunity, ordering Mighton to finish the hedgehog off with another rocket punch. Tails is nearby, a twinge of horror and concern flashing through his mind as he watches. He knows that he'd made a perfect storm of mistakes that had coalesced into this one outcome, and now he's at a crossroads— either he hesitates again and lets Sonic get killed for certain, or he destroys Hypno-bot and ends this crisis once and for all.
But in an instant, Tails finds the strength within to do what he must, because ultimately, no creation of his would ever be able to take the place of his closest friend.
As time runs short, Tails charges towards Hypno-bot, sheer determination pushing him as fast as his tails can spin. His allies keep the enemy robots off him and deflect Hypno-bot's gun just before it fires, ensuring nothing halts his approach. As he finally gets close, Tails, letting loose a loud battle cry, lifts his wrench and slams it down on Hypno-bot's hypno-ray, breaking it clean off. Hypno-bot's control is lifted from all robots once again, and Mighton, once again under his own power, recalls his rocket fist, which stops mere inches short of ending Sonic. Hypno-bot crackles and convulses before going offline. With one decisive move, the turmoil is at last over. The world is saved, and all of the heroes cheer in victory. Eggman, knowing when he's beaten, wisely decides to call it an early night and run with his tail between his legs, along with the few robots he has left.
Later, with the danger now well behind the heroes, Team Cybonic says it'd be best if they stayed in Morristown as its protectors, with Cyborg Sticks arguing that they'd just get corrupted and take over if they were to go down to the surface. Sonic assures everyone that Team Sonic will return if Morristown ever needs their help again. But about that name— it turns out Mighton and Bolts, having gotten a lot of feedback over the day, decided to take everyone's advice and change it; Morristown is now Roboken, and Team Sonic can agree that that's a much better name. The citizens of the newly-christened Roboken are once again able to live in peace, so Sonic and co. are no longer needed. They board a ship, and the robots, FriendBot and the Cubot prototypes having joined them, wave goodbye to their flesh-and-blood liberators as Tails pilots the ship out of the city in the clouds and back down to the surface (and Knuckles activates his seat's vibration function).
It's been a very exhausting day for Team Sonic, but now they can clock out and return home at last. When they get back to the surface, you can be sure they'll get in some well-deserved R&R after all this trouble... until Eggman inevitably attacks again. They might have cancelled the robo-apocalypse, but a hero's work is never done; however, they'll keep up the fight, safe in the knowledge that they've come out of this particularly intense adventure as the victors.
This episode contains examples of:
- Big Bad Duumvirate: Eggman and Hypno-bot team up to conquer Morristown and vanquish their enemies.
- Comically Missing the Point: When Bolts suspects that Amy "wears the pants" in her and Sonic's "relationship":
- Digging Yourself Deeper: Sonic, in regards of hiding his feelings for Amy when she arrives.Sonic: Amy! I'm so happy that you're here, I mean in a totally non-romantic, comrades-in-arms kind of way.
- Game-Breaking Injury: The leg injury Sonic suffered in Part Three comes back to haunt him here, because once a hypnotized Mighton's nailed him with a rocket punch, it has him feeling the pain all over again and prevents him from moving. Hypno-bot takes full advantage of the injury and orders Mighton to finish him off with another punch. If Tails hadn't disabled Hypno-bot just in time, the hedgehog would be a goner.
- Know When to Fold 'Em: After Hypno-bot is defeated, Eggman decides pressing the attack isn't worth it with so many do-gooders around to stop him and gets out of there.
- Oh, Crap!: Played for Laughs; this is Sonic's reaction when Amy reminds him "[they] have that..."
- Story Arc: This episode is the finale of an overarching plotline taking place over the course of four episodes.