Battlegrounds, Part 1 is the twenty-fifth episode of Transformers: Robots in Disguise. It is the first-part of the season finale for the first season.
As Optimus prepares to return to Earth to face the mysterious "evil" he's prophesied, the Bee Team must prevent Steeljaw's pack from teleporting that same threat onto Earth.
Sideswipe sprints through the woods, but is soon knocked down mid-stride by Strongarm, who has managed to track him even while he's running. Strongarm attempts to help him up but he rejects her offer. He tags her back and runs off angry, but when she catches up with him, Sideswipe is caught and knocked out by Thunderhoof and Underbite.
In the Realm of the Primes, Optimus Prime's training is still ongoing, and he rescues a holographic human from an island in the middle of a lake of lava by shooting down some flying drones and using them as stepping stones. Micronus is not surprised and says Optimus is still unready, however the environment suddenly darkens and crackles with lightning; a sign, Micronus says, that the time has come with Optimus still not prepared.
As Strongarm attempts to flee from Underbite, she contacts the base as she was running, but walks straight into a trap set by Fracture's Mini-Cons Divebomb and Airazor. The Decepticons start heading back to base with their prisoners before they could call for assistance. In the scrapyard, the Autobots are alarmed at Strongarm's transmission suddenly cutting off and Bumblebee realizes that they're going to have to mount a rescue. At his suggestion, Fixit searches for nearby sites the Decepticons might be using as a base, and the Mini-Con finds a steel mill. As Denny argues that he should go too, since the team's numbers are depleted, Windblade arrives having been drawn to the place as she revaled to them. She goes on ahead to scope out the mill and the other Autobots follow on the ground. Fixit activates the scrapyard's security system. Steeljaw is for once pleased with his team, though the Decepticons puzzle over what the "First Decepticon" wants with the electronics they've collected. Steeljaw is more interested in freeing the captive Decepticons in the Scrapyard, and sends Fracture to go capture Fixit. The visage of the first Decepticon appears to Steeljaw once again and demands he complete the device required. Thunderhoof and Underbite watch as it appeared to them Steeljaw was talking to a wall. When Steeljaw is insistent on freeing the Decepticons first, the first Decepticon tortures Clampdown (much to the amusement of Thunderhoof) until he changes his mind. Steeljaw told him to cease from torturing his comerade and Clampdown was released. The first Decepticon informs him that they need a metal mass of sufficient size to dissipate the energy caused by the first Decepticons transition into the material universe.
Micronus takes Optimus to the Primes, who are disappointed that Optimus is yet unready. Optimus convinces them to send him anyway. They imbue him with a portion of their power, upgrading him into a new form. Micronus was impressed and Optimus was fully upgraded.
Windblade reaches the steel mill but is knocked out of the air by a flying chunk of metal thrown by Underbite. While the other Autobots speed up in an attempt to go to her aid, the Decepticons are already making off with her.
Fracture reaches the scrapyard, but the security system gives him pause. Fracture watches as Hank arrives to give Russell a spare Bronko Kowalski trading card, and Russell manages to convince her that it's unsafe to enter the scrapyard as they're spraying for bugs. The other Autobots fruitlessly search the steel mill, however Drift finds clues which put them back on the Decepticons' trail. Russell's called back to the gate by Hank, who convinces him to open the gate in order to give her the card without any damage to it. Unfortunately for him, this Hank is actually Airazor with a holographic disguise. Holding Russell hostage, Fracture demands Denny turn over Fixit. The Autobots find that the Decepticons have chained their captured comrades to the Crown City Colossus and are erecting a huge and ominous archway in front of it. Fixit confronts Fracture by firing a shot that enables Russell to break free from Airazor's grip and manages to help Denny and Russell escape the Decepticon's hands. The trio take shelter in the diner. Grabbing weapons, they rush out to make a final stand against their foes, only to find that the Decepticons have already been defeated by Optimus Prime. Russell was impressed by this and Optimus notes about them before asking for Bumblebee. Denny informs him about Bumblebee going to rescue the others from Steeljaw's pack. Fixit detects their location as Russell convinces Optimus to take him and his dad along to find the grave evil he's come to face.
At the statue, the first Decepticon demands the process begin to bring him into this universe. The three captive Autobots recover consciousness, but find themselves in agony as Steeljaw activates the arch. On the other side of the river, Bumblebee and his team start moving in. The Decepticons spot Bumblebee and Drift incoming, and when the pair arrive they're faced by Thunderhoof and Underbite. Grimlock arrives having taken a more direct route, but is prevented from destroying the arch by Clampdown. Above them, a huge vortex forms and a portal opens within the arch, through which a form begins to emerge. Optimus himself also arrives, and manages to destroy the arch. It explodes, sending everyone flying, however Optimus is too late: Megatronus has made it through the portal.
"Drift, Grim, let's roll to the rescue! Wait, no, somebody's already using that battle cry."
- —Bumblebee apparently remembers the Rescue Bots.
"Dis is what I call entertainment!"
- —Thunderhoof enjoys Clampdown being tortured.
"Micronus, the crisis is upon us, and we sense our chosen champion is not prepared."
"If innocents are threatened, preparation comes secondary to swift action, determination and will. Send me to Earth, please."
- —Vector Prime and Optimus Prime
"Our oafish teammate's enthusiasm is as large as he is."
- —Drift on Grimlock
"At long last, Megatronus stands triumphant!"
- —Megatronus has come to mess scrap up
- Megatronus first manifested to make his deal with Steeljaw in "Lockout", though his identity has remained a mystery until now.
- Though only Vector Prime is identified in the group shot of the shadowy Primes, we can identify a few based on their features. The beard of the leftmost Prime suggests Alpha Trion, the braided hair of the Prime second from left is most likely Solus Prime, while the rightmost one resembles Quintus Prime.
- True to form, Optimus Prime once again gives death the middle-finger and returns to the mortal plane. He ALWAYS comes back.
- In stasis: Hammerstrike, Bisk, Chop Shop, Terrashock, Filch, Minitron, Springload, Ped, Quillfire, "that one with all the eyes", Malodor and the Skunkticons, Nightstrike, Vertebreak, Octopunch, Groundpounder, Headlock, Scowl, Scratch, Zizza, Pseudo
- Known at large: Steeljaw, Thunderhoof, Underbite, Clampdown, Kickback
- Released: Grimlock
- Countless others all missing, presumed at large
- Bumblebee orders his team to "roll to the rescue", but then remembers that "someone else" is already using that catchphrase.
- Only appearance of Bronko Kowalski. (Photograph)
- Last appearance of Fracture, Airazor and Divebomb.