In a secret subterranean factory, the Autobots and their human allies work diligently on their "Scramble City" project, constructing a giant mobile fortress under the direction of Ultra Magnus. When the Decepticons detect magnetic fluctuations emanating from the concealed base, however, Soundwave`s cassettes investigate; despite resistance from Blaster and his tapes, Ratbat manages to penetrate the cavern and discovers the construction work. Megatron dispatches Starscream, Thundercracker, Skywarp and the Constructicons to attack the factory, but their way is barred by an Autobot contingent led by Optimus Prime. When Ultra Magnus, monitoring the battle from the base, sees the Constructicons merge into Devastator, he sends the Aerialbots to join the fight. Their added firepower fells Devastator and sends the Decepticons retreating, and in retaliation, Megatron deploys the Stunticons. The Autobots roll out to confront them, and the battle soon escalates as the two combiner teams form Superion and Menasor. Using Scramble Power, the two super robots shift their limbs for optimum power, but after a few reconfigurations, Fireflight gets confused and attempts to connect as the wrong limb, crashing into his team-mates and falling off. Menasor seizes the opportunity and disengages Dead End, who attaches as Superion`s leg, with painful results for the air warrior. Optimus Prime takes action, blasting Dead End off and allowing Fireflight to recombine with his team, at which point the Combaticons arrive to tip the battle in the Decepticons` favor as Bruticus. Back in the Autobots` factory, Scramble City has finally been completed, and Ultra Magnus has it transform to mobile fortress mode and sends it to join in the battle along with the Protectobots. Menasor and Bruticus have already defeated Superion as the team arrives, but as Defensor, they protect the other Autobots as Scramble City transforms into its robot mode - Metroplex! A single blast from Metroplex`s cannon defeats the two Decepticons, but as the Autobots celebrate their victory, the nearby ocean parts, and from its depths arises Trypticon!