In a mountainous valley, down a cavernous waterfall and beneath the surface of the Earth, something rather insidious is taking place. The Constructicons are making use of a drill to burrow through a rock, but it fractures and risks danger of exploding and killing them all or something. Mixmaster saves the day by sealing it up and then they all fire at it with their lasers until it seals.
Megatron berates the lot of them for not sensing the chance of the rock fracturing, while Starscream berates Megatron for coming up with such a zany and dangerous scheme, but his leader reminds him that if it succeeds, they will have an energy source greater than anything in the galaxy! And what would that happen to be?
The core of the Earth! Yowza.
Starscream gives Megatron some geographical education by using a boulder as a demonstration: The Earth is spherical, so to corrupt it's inside would make it explode and kill everything on it, even them! Megatron replies merely with "you underestimate me, Starscream" as they return to the surface and make their way through a holographic wall, wherein lies a space bridge to Cybertron! That's the health and safety matter sorted, so the Decepticon leader is given the chance for some glowing eyed laughter.
Gears, Mirage, Jazz, Sunstreaker and Prowl
are on the patrol of the valley when they realise that a river that used to be
here is gone. They take an alternate route and find that the river has merely
been diverted into a canyon. A canyon where the Constructicons are hanging out!
Mixmaster and Scavenger return to base while the Autobots follow after, only to lose their trail. Laserbeak spies them and returns to Soundwave. He informs Megatron of the sighting of the Constructicons and this prompts them all to return to the surface to make sure the Autobots don't inform Prime of this.
The Constructicons form Devastator, take hold of a boulder and throws it at the Autobots, sending all but Mirage plummeting to the rocks below, who's sent down with an optical laser from the combiner. He manages to grab hold of a branch and makes himself invisible before it inevitably snaps.
Devastator jumps down after his prey while the four Autobots open fire, but they're subdued in no time. Mirage, however, manages to sneak inside the drilling base and takes note of what's going on, so deems it important to report it to Autobot HQ.
Before he does that, he returns to his buddies and throws Mirage his grappling hook while Jazz distracts Devastator with some projectile visuals. While the big lug is dazed, they tie his legs up and send him tumbling down, allowing them all to escape with no hassle whatsoever.
Optimus becomes aware of the drilling
operation and fears the consequences, so stopping it is their primary goal; but
Prowl reminds him that Megatron has Devastator and he's a hard cookie to
crumble. Chip Chase rolls in to inform Prime of an invention he and Wheeljack
had been working on: Dominator discs. If they manage to put one of those on each
of the Constructicons, then Devastator will be under Autobot control! Prime
arranges a commando team to undergo the mission at night.
Prowl, Jazz, Wheeljack, Sunstreaker and
Mirage make their way down the waterfall which Ironhide freezes, thus
overheating the drill. The Constructicons immediately cease drilling and return
to the surface to see what caused this blunder...
Allowing the hiding Autobots to plant dominator discs on each and every one of them, using such crafty tactics as hiding in holes or shooting them from guns or throwing them like Frisbees. All of the Constructicons are planted with the discs, so the Autobots head back up the cliff in a wire-suspended cage...
Which Starscream is aiming to shoot down!
This commercial break suspense is ruined by Megatron taking the gun from Starscream and asking why destroy six Autobots when they can eliminate them all? Megatron is apparently aware of the Constructicons having the dominator discs planted on them, but refuses to explain his plans right now, instead focusing on the inevitable attack the Autobots will make.
The Autobots arrive but the Decepticons are waiting for them, unleashing fire from the front, missiles from the sky and all kinds of warfare. The Autobots fight back, but it's all just delaying the foreseeable use of Devastator...
Who when summoned, promptly starts kicking Autobot ass. He takes Prime in his hands and looks ready to crush him (or at least gloat) before Wheeljack drives by with Chip Chase, who activates the dominator discs.
The combiner recoils while Optimus commands him to put him down and attack the Decepticons. And he obeys! He clobbers the Seekers and fires at Megatron, forcing the bad guys to retreat back to the drilling base which only allows the combiner to blast the roof above it and seal them in with boulders. Ironhide insists they go in and finish them off, but Prime sees no reason to; they're trapped and have no water to power the drill, so that gives them the perfect opportunity to head back to base and get repaired.
In the cave, Starscream goes back to berating Megatron, but he pulls a trick from his sleeve: An electronic disrupter, which will scramble the Constructicons' circuits and make them resume killing the Autobots when they least suspect it! And he also stored enough water for the drill to make it's final thrust to the Earth's core, not to mention the Autobots are still oblivious to the space bridge, so they can still proceed as planned!
Back at the Ark, the Constructicons are helping the Autobots by repairing their wounded, but an earthquake shakes things and makes them aware that the drilling is still operational, so they roll out to bust their asses.
Arriving at the valley, Devastator busts open the cave entrance and allows the Autobots to head inside.
Devastator is commanded to destroy the drill, but Megatron uses the electronic disrupter to resume their usual evil personalities, allowing the combiner to open fire at Prime and Chip, the latter of which makes a getaway but gets himself sealed in a cave via falling rubble.
Although the Autobots are all out for the count before the commercial break, they're back on their feet afterwards and backing away from Devastator, but the real danger is that the drill is reaching the Earth's core! This sends more tremors through the ground and knocks over the water supply, as well as unblocking the cave Chip was in and allowing Sunstreaker to rescue him.
Wheeljack tries to regain control of Devastator, but Chip warns him that doing so could overload his logic circuits. This happens and sends him into a frenzy of destruction, throwing Starscream into a computer console and damaging it, thus sending the drill out of control!
The Decepticons flee to the space bridge, but Devastator doesn't his abandonment very well and flies through the roof and destroys it, thus making them all as doomed as Earth itself! Megatron claims they'll be safe if they can stop the drill before it all goes boom, and Wheeljack pops in to inform them that's precisely what he was thinking of.
Prime persuades Megatron to hand over the electronic disrupter so they can combine the frequencies and make Devastator not so crazy; he agrees reluctantly, but Starscream naturally has to prove he's wrong and screams to Devastator for help, only to get blasted. Wheeljack and Chip set to work on it and eventually bring the big lug to his knees, separating him into his six components.
With only two minutes until the Earth dies, the Constructicons start talking like inspirational posters before becoming Devastator again and chasing after the drill. He reaches the end and begins pressing against it, and after a mild struggle, breaks the drill entirely, but not without forcing some lava up to swallow the rest of the drill.
The Decepticons fled the scene before the day was saved, though, and Devastator arises to see them missing, asking where his master went. Chip informs him that his noble master is busy saving his own skin, but Devastator refuses to believe this before making his exit.
Chip, however, is sad that Devastator is back with the Decepticons, and was hoping for him to remain an Autobot, but concludes that it was probably a "dumb old dream." Prime tells him to "hang onto your dreams, Chip. The future is built on dreams. Hang on."
Prowl's white is coloured the same grey as that on Bluestreak in this episode; the only way to tell them apart is Prowl's police decorations and having black instead of Bluestreak's darker grey.
This episode shares the same style of wonky animation as The Autobot Run and City of Steel, meaning they were all probably done by the same animation studio.