Microbots

Megatron recounts the discovery of the Heart of Cybertron, a power source that once drove him to madness, as the Autobots shrink down to retrieve it.

While digging for Maya artifacts in South America, a group of archaeologists stumble upon an ancient spacecraft. As news of the discovery is broadcast on the news, Soundwave and Megatron recognize it as the Decepticon ship they traveled to Earth in four million years ago. Megatron states that there is something on that ship which he wants, and sets out to get it.

Meanwhile, at the Autobots' headquarters, Perceptor is using a shrinking-enlarging device to repair one of Ironhide's memory chips while being insulted by Brawn for not being a soldier. Bumblebee walks in and tries to make him stop, when Optimus Prime orders Brawn and Bumblebee to follow him to South America along with Ratchet, to stop Megatron from obtaining what he wants.

As Megatron's troops blast their way through a rainforest in order to avoid satellite detection, Starscream manages to first miss blasting a tree and then get attacked by a giant snake, to the amusement of Rumble and the Constructicons. Meanwhile, Ravage has met his match in the form of a real jaguar, which attacks him but Ravage slaps it and it flees. The Autobots arrive and decide not to burn the forest down, because Optimus says "that's not our style".

Megatron gets through the forest first, and reaches the ship. Blasting it open, he retrieves the ship's energy core, the Heart of Cybertron. Hook implants it into Megatron's torso, vastly increasing his power level. Optimus Prime then arrives and orders the Autobots to attack, but they are all defeated by Megatron's new ability to continuously fire energy from his fingertips. The Autobots only manage to escape when Optimus orders Smokescreen to generate a smokescreen, allowing them to bring a hill down on the Decepticons.

After limping back to base, Wheeljack creates a force-field to keep Megatron at bay. Perceptor hatches a plan to shrink himself, Brawn and Bumblebee to microscopic sizes in order to infiltrate Megatron's body and disconnect the Heart of Cybertron.

Meanwhile, the Decepticons sit around and get plastered overcharged on energon. After Megatron rambles on about the "good ol' days" and passes out, Powerglide delivers the tiny Autobots into his body. This wakes up Megatron, who fires a few parting shots at Powerglide. Finding that none of his warriors can even stand up (or in Laserbeak's case, fly straight), Megatron departs to destroy the Autobots himself.

Perceptor, Brawn and Bumblebee make their way through Megatron's body, avoiding his electro-sanitizers, until they reach the Decepticon's brain. The others have to restrain Brawn from destroying the brain, since the fall would likely cause the Heart of Cybertron to explode. Megatron reaches Autobot headquarters and begins firing on the force field protecting Optimus Prime. The miniaturized trio ride one of Megatron's evil brain impulses to the Heart of Cybertron, which Perceptor disconnects while dodging more brain impulses. Taking the heart, they make a dash for safety as the shrink-ray's effects begin to wear off. Megatron, deprived of his weapon and knocked flat by Optimus, is shocked by the sight of three rapidly-growing Autobots jumping out of his shoulder joint, and flies off.

Observing that the Heart of Cybertron has become unstable, Brawn tosses it two thousand miles into the sky, at which point Perceptor detonates it with a blast from his cannon. After this, Brawn shows much more respect for Perceptor.

—Rumble and Scavenger are why we can't have nice things.

—Rumble and the Constructicons laugh at Starscream.

—Ratchet and Cliffjumper debate whether or not to attack the powered-up Megatron.

—Brawn is just being pissy at this point.

—The Decepticons give us what is quite possibly the intentionally funniest scene in the series.