The Metal Men are returning to Earth, after a prior adventure on another world. Platinum had provided the inspiration for that world's robot slave population to rise up against their enslavers. The Metal Men's ship is caught in a meteor storm. One meteor breeches the ship's shields, becoming lodged in the hull. With the majority of the Metal Men still recovering from the slave uprising, Doctor Will Magnus goes out on the hull, himself, to dislodge the meteor. Platinum follows. Platinum prevents further meteors from hitting Magnus, sustaining heavy damage. Magnus carries Platinum back on board the rocket ship, to begin repairs. By this time, the other Metal Men have revived. Gold notices that Magnus' space suit has been compromised, and worries about potential exposure to cosmic radiation. Magnus brushes off the Metal Man's concern. In the days that follow, Magnus begins to undergo a transformation, eventually becoming a robot himself.
Platinum is beside herself with joy, believing that she and Magnus can finally be together. Her fantasy of a perfect life with Magnus is shattered, though, when Magnus, as a robot, proves to be far less emotional than the Metal Men. Coldly, Magnus rebuffs Platinum's advances, then orders the Metal Men to make themselves useful. Pulling Tin aside, Magnus threatens to scrap the humblest of the Metal Men, unless Tin can prove his worth. While the Metal Men busy themselves with their various tasks, their attention is drawn to another rocket ship, being pursued by a comet-like creature. Gold requests permission to intervene, but Magnus commands him to stand down. Disobeying thier creator, the Metal Men set about to rescue the imperiled crew of the rocket ship. Lead molds himself into an enormous hand, and grabs both the rocket and the creature. Lead leaves just enough of a gap, in the hand, for the creature to pour through.
Tin molds himself into an enormous cup to catch the comet-like creature, but proves too fragile to hold it. Mercury tries to restrain it by molding himself into a barrier, but in the frigid cold of space, Mercury is rendered brittle. Platinum weaves herself around the comet creature, and draws it into Gold. Iron then pounds Gold wafer thin, destroying the creature. Magnus is furious at the Metal Men's disobedience, and threatens to scrap them all, upon their arrival on Earth. As soon as they reach their headquarters, the Metal Men lock Magnus in his laboratory. The team then sets about searching for a solution to transform Magnus back into a man. While the Metal Men run their experiments, Magnus has time to cobble together a new team of robots, based on gases instead of metals. Once fully operational, the Gas Gang blasts their way out of Magnus' laboratory. Chloroform leads the attack against the Metal Men, flooring them with laughing gas.
Gold forces Oxygen to clear the air, only to see himself, and the other Metal Men, begin to rust from the oxygen exposure. In the face of imminent defeat, the Metal Men fall back. Lead forms a barrier between the Metal Men and the Gas Gang, giving the Metal Men time to flee. Carbon Monoxide and Carbon Dioxide double team the fleeing Metal Men. Staggered by the assault, the Metal Men barely make it into Magnus' laboratory. There, Helium expands to monstrous size, trapping the Metal Men within the laboratory. Gold plugs himself into the wall, then binds the Gag Gang, along with Magnus, together. Gold's body conducts extreme enough heat to vaporize the Gas Gang. Magnus' inert body is moved to the robot recovery room, where, over time, the effects of the cosmic radiation fade. Human once more, Magnus, uncharacteristically, returns a bit of Platinum's affection.