The Ultimate Doom, part 3

With Sparkplug setting off the alarm the Autobots have to go and Spike tells his Dad that they'll find some way of saving him. But then Shockwave, Soundwave and some seekers arrive, but amazingly Brawn manages to knock both of the seekers out of the way and then shoots at Soundwave.
 

Soundwave gets hit but before Spike and the Autobots can escape, Sparkplug blocks off the exit. Shockwave then actually does something useful once, even managing to shoot Brawn and he and the other Decepticons present surround the Autobots and are about to destroy them when...
 

...suddenly a wall explodes blasting the Decepticons out of the way and in step Skyfire, Trailbreaker and Wheeljack, who easily beat down the Decepticons and give enough time for everyone else to escape back to the outside, but they still haven't managed to save Sparkplug and now the entire Decepticon army knows that they're on Cybertron.
 

The Autobots are chased by various Decepticon drones and seekers but all of them bar Skyfire get to Wheeljack's workshop, and Bumblebee shows everyone a disc he swiped from the Decepticon complex. Wheeljack puts the disc into a computer and the data on it reveals more information about how the hypno-chip works.
 

Back on Earth Optimus Prime and a few other Autobots are surfing towards where the Decepticons are. Megatron has a plan to get a tidal wave to crash straight into a couple of generators, which will create lots of energon for the Decepticons to take. When Dr. Arkeville hears of this he tells Megatron to call it off as all of his slave workers will drown, but Megatron just says something hilarious. As the tidal wave approaches Megatron also warns Arkeville to stay away from Cybertron, but Arkeville thinks that Starscream may be the real ally he wants.
 

The Autobots arrive but the tidal wave is right behind them and knocks them all out of the way as energon is created. The Autobots quickly pull themselves together and re-group but it's too late as they can only watch as Megatron gets away in a ship full of energon cubes. They can't even go after him right away as they have to stop behind to save all of the human workers.
 

Dr. Arkeville soon finds out that Megatron has left him behind and hangs on for dear life on a piece of metal. But Starscream has also been left behind and informs Arkeville that Megatron is through with him, but he isn't. And with that Starscream grabs Dr. Arkeville and shoves him into the cockpit of his fighter jet mode as he transforms and takes off.
 

Back at Cybertron Wheeljack has created a device which will hopefully nullify the effects of the hypno-chip and radios Optimus Prime on Earth to update him on what they're up to. Later on Spike goes back to the Decepticon base and is soon found by Shockwave who grabs him and demands to know where all of the other Autobots are.
 

And they're right behind him as Wheeljack presents forward his new invention and turns it on. It works and Sparkplug is freed from the influence of the hypno-chip Dr. Arkeville had put on him and he and Spike start to run out of the complex as the Autobots fire at the Decepticons before they start to retreat also. Shockwave sends seekers after the Autobots.
 

The Autobots make it back outside alive but are pinned down by Decepticon turret fire, until Wheeljack contacts Skyfire and has him shoot it all. The Autobots then climb aboard Skyfire who takes off and heads back to Earth as their mission to save Sparkplug is finally complete.
 

On Earth Megatron is having a load of human slave workers load his ship with energy, completely oblivious to the small fact that Optimus Prime and the other Autobots are watching him from a far. Megatron then hears a noise and finds Starscream attempting to drain energy from Dr. Arkeville's brain so Starscream can power himself up to take control of the Decepticons, but his plain isn't working. Megatron is about to kill Starscream for his treachery when Skywarp reports an emergency and Megatron finds that the slaves have malfunctioned - they are going in and out of the ship without dropping off the energon cubes. As Megatron is distracted, Starscream and Dr. Arkeville sneak off.
 

The Autobots then start their attack but things don't go to plan as they're outnumbered badly. They need reinforcements and they need them now!
 

And that's the point where Skyfire arrives. Wheeljack uses his machine to free all of the humans in the area of Dr. Arkeville's mind control and then Skyfire drops the Autobots off to join the fight. But Megatron suddenly leaves in his ship telling Optimus he can die on Earth as he heads back to Cybertron with all the energon he needs. The other Decepticons retreat too but the Autobots start to fire at Megatron's ship -the only chance to stop the disasters on Earth is to knock Cybertron out of it's orbit and to do that they need to create a huge explosion, and if they destroy Megatron's energon filled ship they just might be able to do it.
 

Megatron's ship takes a battering from Autobot fire and some shots blow up the energon cubes he has onboard. The ship blows up in the massive explosion the Autobots needed and as they predicted, Cybertron is blown out of the Earth's orbit. The planet is saved and the disasters like tidal waves cease.
 

With the Earth safe, Spike says they've done a great job by saving the Earth, moving Cybertron, getting Sparkplug back and destroying Megatron, but Optimus Prime in uncertain on the fate of his arch-enemy. And sure enough, Megatron has survived the explosion and says he'll be avenged before flying off back towards Cybertron.

The subtitle for this episode in the script is "Revival".

Countdown to Extinction is practically The Ultimate Doom, part 4 in everything but name, and shows us what Starscream and Dr. Arkeville get up to.