A lunar rover examines recent seismic activity on the Moon's surface and stumbles upon the crashed Nemesis. As it moves in for a closer look, a huge, unidentified object lands on the rover and crushes it. The huge thing turns out to be Lugnut. His partner, Blitzwing berates him for his clumsiness, but then offers some dancing lessons. An annoyed Lugnut points out they've traveled across the galaxy to find Megatron's ship, not become light on their feet. Blitzwing comments that this is the same sector in which they lost track of Lockdown, and an argument breaks out (Lugnut doesn't like Lockdown), culminating in Lugnut confidently stating he knows Megatron still lives...
On Earth, Ratchet is rudely awakened from a stasis nap by an unapologetic Sari, who is in the middle of a street hockey game with Prowl, Bulkhead and Bumblebee. The game picks up, and Bumblebee is about to score, when a trash can makes a save! Sari tries to write it off, but Ratchet is quick to notice the key currently plugged into said can. He tells her off, but they are interrupted when the key begins to glow, followed by two glowing objects entering Earth's atmosphere. As a prophetic Ratchet decides this can't be good, camera-bots move in to investigate, but are quickly crushed by Blitzwing. Both he and Lugnut mistake a nearby crane as a sentient life form, and Lugnut demands to know Megatron's location. After a shove, the crane responds by slamming its wrecking ball into Blitzwing. Watching a live feed, Megatron muses over whether or not he can risk revealing himself. After all, he has already been betrayed once. At their home base, the Autobots get ready to mobilize. Sari is all fired up, but both Ratchet and Prime tell her she needs to wait behind, as they want to protect the innocents. (Bumblebee very quickly points out that they're innocent too.)
Back at the construction site, Blitzwing and Lugnut have decided to devastate the place in order to draw out the Autobots. It works, and things quickly kick off as Optimus is forced to slice a tanker thrown by Lugnut in half. This promising opener falls apart when Blitzwing prevents both Prowl and Bumblebee from launching any attacks. Ratchet manages to trap some of Lugnut's missiles (though they break through his magnetic grip, they still don't hit any of the Autobots), but as Bulkhead tries to outmuscle the massive 'Con, Lugnut proves to be too powerful and throws him aside. The combined efforts of Blitzwing and Lugnut prove too much for the Autobots, and things go from bad to worse when they tell the Decepticons that Megatron burned up "over Cleveland". A raging Lugnut activates his rocket fists and levels the entire area, flooring the Autobots and burying both himself and Blitzwing.
As the Decepticons free themselves, Megatron becomes convinced of Lugnut's loyalty and opts to contact only him, while Blitzwing tells Lugnut to warn him before using his big punch. Lugnut automatically decides to abandon the battle and answer the summons, dragging Blitzwing along and leaving behind some very confused Autobots. Blitzwing headbutts Lugnut in midair, and Lugnut responds in kind, slamming Blitzwing down into an army base. He explains he heard Megatron's voice, but Blitzwing merely hears approaching police. He suggests they scan local vehicle modes and hide, but Lugnut refuses until Megatron orders him to do so. He quickly scans a bomber, while Blitzwing, after a quick argument with himself, scans an assault tank and a fighter jet. Captain Fanzone arrives, but the Decepticons are already hiding in plain sight.
The Autobots have returned to base and are making repairs. The constant danger of attack makes Prime decide the best thing to do would be to repair the Ark and take the AllSpark off of Earth. Sari takes this very badly, and she is most unwilling to use the key to help Ratchet fix the ship. For his part, Ratchet is less then pleased about having to work with a "protoform". Prime settles it by ordering the two to be partners.
Meanwhile, Lugnut and Blitzwing are perched on a blimp, observing the city below. As Blitzwing comments on the local wildlife, Megatron transmits information on the key to Lugnut and orders the retrieval of it and the AllSpark. Lugnut immediately transforms, followed by a less-than-willing Blitzwing.
At Lake Erie, the Autobots arrive, with Ratchet and Sari still bickering. They are quickly interrupted by Blitzwing and Lugnut. Ratchet and Sari make a break for it, but Blitzwing freezes the lake, preventing them from reaching the ship. However, they get a hand from Lugnut, who accidentally blasts a hole for them to get through. The Autobots dive in, and as Ratchet heads for the Ark, Lugnut and Blitzwing are stalled by the rest, thanks to some clever thinking from Prime. In the Ark, Ratchet has a moment alone with the ship, but ends up fighting with Sari, who storms off to the AllSpark's cargo bay. Dejected, she gets the idea of damaging the ship enough to prevent it flying, but the key quickly repairs it. Suddenly, the AllSpark opens to reveal an image of Megatron's head and the key. Moments later, a fully restored Megatron materializes, and a terrified Sari panics and opens the airlock. As water pours in, Ratchet manages to save her. Sari confesses to her sabotage, but a sympathetic Ratchet explains the reason he wants to leave is because he cares about the planet and its people...especially Sari.
Finally understanding, Sari agrees to help. Ratchet reveals the ship was originally a military vessel, and he hopes to bring the weapons bay back online. Outside, the Autobots are in serious trouble, but Sari's key soon reactivates the weapons bay, and Ratchet tells Optimus to draw the Decepticons to the Ark. As they close, he activates the main cannon and blows the pair of Decepticons to kingdom come. A furious Megatron loses his link, and the Decepticons crash down onto the surface of the lake in several badly damaged pieces.
Back at base, Sari uses the key to patch up Bumblebee, acting rather Ratchet like when he asks for some customization. Ratchet reveals that even with the key, it'll take some time to get the ship up and running, so they won't be gone for a good while, and Sari smiles happily.
At the lake, Blitzwing calls for help, while Lugnut begs for a sign of Megatron's forgiveness. Remarkably they get a sign-a bad one, as Starscream shows up, promising repairs...in exchange for loyalty.