Episode 4 of Transformers Prime, Darkness Rising part 4 first aired on December 2nd 2010 on The Hub. The episode begins with a look back over episode 3 before continuing the scene with Ratchet and Optimus Prime comign under attack from Megatron's zombie army. No sooner has the action begun than the scene shifts back to Bulkhead who quickly has to save Raf and Jackson from a Decepticon attack. Bulkhead tries to leave the Humans behind before scalling the mountain side and climbing onboard the Decepticon ship, taking some mor eEradicons with him. No sooner does the big green bot get a chance to rest an Miko starts banging around inside him. She hid when he transformed and so has once again stowed away. Before Bulkhead can have words with her the pair once again become under attack from the Eradicons and eventually seek shelter inside the Decepticon ship itself. Whilst this is going on, Jack and Raf have become caught by the Decepticon and are also now onboard the ship. The Eradicons are ordered to take their prisoners to the cells where Agent Fowler is being held. However before the Decepticon drones are able to carry out that order, Bumblebee and Arcee appear from no-where and recsue the two Humans before meeting up with Bulkhead. Raf and Jack explain that they know where Agent Fowler is being held.
We shift to show Agent Fowler being threaterned by Starscream who is interrupted by the sound of fighting. He orders some more Eradicons to go and find out what is going on before returning to question the human regarding the location of the Autobot base.
We then jump back to Optimus Prime and Ratchet who have turned the battle into a hand-to-hand contest with the zombie-bots. Both Ratchet and Optimus Prime become over-powered by the Decepticons and just as it is looking like the zombies are going to finish off the doc-bot, than Prime summons the strength to fight back, freeing himself and saving his comrade.
Meanwhile, back onboard the Decepticon ship, the Autobots leave the Humans in a room and head off to save Fowler. When they find him there is a breif stand-off between the Autobot's and Starscream until Fowler causes a distraction and the good-guys gani the upper hand causing Starscream to flee. Whilst this is going on the Humans make a discovery of their own. A mathmatical equasion on a Decepticon screen. Raf tries to copy the data but is spotted by a Decepticon and the three kids have no choice but to flee but not before Miko takes a photograph of the Eradicon and then of the forumla on the computer. The Humans quickly run into the Autobots who once again have to save them before we shift again.
The next scene picks up where we left of with Optimus Prime and Ratchet defeating the last of the Zombie horde and scaling a cliff after Megatron who transform and flies off, but not before telling the Autobots that this was just a test and that his real plan is yet to come. The two bots are left pondering what on Earth could the Decepticon leader have instore in this was just a test!
Time jumps and all of the Autobots and Humans are once again back in the Autobot HQ. Bulkhead gets in trouble for taking the humans with him, though Miko tries to stick up for her guardian. After passing on the image, Jack announces that he has had enough and wants out and so is transported home by Ratchet whilst the other Humans stay behind.
We jump back to the Decepticon ship one last time where an irrate Megatron is beating on Starscream. Just as Megatron is about to extinguish Starscream's spark, the wiley Decepticon manages to talk his way out of it.
We jump back to Earth and Jackson's garage where he is fixing his 10-speed when Bulkhead and Miko turn up. Miko tries to talk Jackson around but he is having nothing of it and expresses his desire to stay out of it.
The scene changes one last time back to the Autobot base where Rathet has decoded the image taken by Miko and announces thay they contain plans for a Space-Bridge! Are the Decepticons looking to leave Earth or, as Prime fears, are they planning to bring reinformance from the one place that has them .... Cybertron!
An so the episode ends with the first CGI image of modern day Cybertron leading us nicely into the next and final episode of the 5-part mini-series