When Quark's Dr. Kirby disappears after an experiment with his Quantum Machine goes awry, a hostile monster emerges and goes on a rampage, apparently having destroyed the doctor. Back at Quark, Rusty discovers a previous ""boy robot"" prototype. Hoping for a new friend, Rusty reassembles the robot, who he names ""Earl."" But Earl's relentlessly aggressive programming turns him against the heroes.
Being powered up for six months, Rusty has not grown an inch. Frustrated that he will never be as big as The Big Guy, he connects his robot head on the powerful robot body of Quark's T-7000 Prototype. But he learns there's more to crime-fighting than just being big when a gang of exosuit-wearing chopshoppers (Gage, Big Rig, and Cargo) lure him into an ambush.
Donovan unveils Quark's latest prototype: tiny liquid metal robots called Nurds that repair and upgrade any technology they come in contact with. When Big Guy becomes infested by the Nurds, they repair its original artificial intelligence circuitry, making Big Guy a fully functioning robot, which removes Dwayne from the pilot's seat. But shortly after the new Big Guy successfully completes his first mission, things go awry.
While trying to keep the Legion Ex Machina's newest robot from absconding with Quarks' new anti-neutrinos, Rusty plugs into the bot's software to learn the Legion's secrets. #4 counters Rusty's hack by engaging in a mental tug of war. A power surge switches personality traits between the two robots. Rusty starts building a doomsday machine while #4 plays video games.