Platinum convinces the overworked Doctor Will Magnus to take a long overdue break. Magnus spends a day at the beach, in the company of his Metal Men. At first, Tin molds himself into a sunshade to protect Magnus from the rays of the burning sun. Tin, however, transfers too much heat to Magnus. Lead, ultimately proves the better choice for protection from the sun. Magnus is only recently back on his feet. After suffering from a strange ordeal that found him transformed into a robot, Magnus turned against the Metal Men. Magnus created the Gas Gang, five new Metal Men, designed to destroy his former creations. Using thermal conductivity, Gold was able to vaporize the Gas Gang. Soon after, Magnus regained his humanity.
During Magnus' convalescence, Platinum grows jealous over the attention Magnus receives from Ava Woods, a beautiful model. In response to Woods' condescending attitude towards her, Platinum pies Woods in the face. In tears, Platinum races out of the room, to be consoled by Tin. Platinum decides to compete in the same beauty pageant Woods is favored to win, to prove she is the more desirable girl. The Metal Men continue the work on one of Magnus' myriad of research projects. This one involves monitoring the sun for solar prominences. Iron tracks a particularly large solar prominence that breaks free of the sun, firing out into space. The solar prominence is bombarded by cosmic dust, impacted by a meteor swarm, and finally, bathed in the radiation of an exploding star.
These three effects cause the solar prominence to transform into a bizarre, multi-limbed creature. It's first act of sentience is to take possession of an unmanned rocket ship. The creature breaks the rocket down into it's component parts, then reassembles them. It then casually hurls the rocket into the path of another unmanned ship, destroying them both. Dubbed the "Solar-Brain" by Gold, the Metal Men inform Magnus of the creatures's existence. Though a potential threat, Magnus can do nothing about the Solar-Brain until the Metal Men can relocate it. With Tin by her side, Platinum garners a dress for the pageant. Fashioning himself into an umbrella, Tin keeps the rain off Platinum, to keep the elements from ruining her dress.
Magnus, as one of the judges of the beauty contest, disqualifies Platinum, on the basis that she is not human. Furious, Platinum attacks Magnus, and Woods, winding herself around and around them. Magnus orders Platinum to let them go. Platinum complies then runs out into the rain, once again consoled by Tin. In a jealous rage, Platinum quits the Metal Men. Gold informs Magnus that they've picked up the trail of the Solar-Brain. Outside the pageant, Magnus meets up with Tin. En route to their headquarters, Tin spies a disassembled skyscraper tumbling down upon them. Tin molds himself into a canopy to protect Magnus, but suffers severe damage. Iron collects Magnus, and Tin. With no time to effect repairs on Tin, Magnus has Iron load Tin's inert body into their rocket ship.
Platinum returns just as the rocket launches into space. Platinum is just able to wind herself around the rocket, before it reaches escape velocity. Gold brings Platinum on board. As an immense fiery meteor hurtles towards the ship, Magnus activates a defensive system called "The Chain Reaction". The meteor is destroyed when it completes the circuit of the chain's deadly arc. The Metal Men encounter the Solar-Brain, as it disassembles an unmanned space station. Inexplicably, the Solar-Brain is also stockpiling every weapon known to man, garnered from museums, ammunition dumps and armories from around the world. As the Metal Men draw near, the Solar-Brain disassembles their rocket ship, depositing the team on a small planetary body.
The Metal Men leap to defend Magnus from the creature. The Solar-Brain repels their collective attack, as well as reducing them in size. The Solar-Brain forces the Metal Men to combine, and mold themselves into a hand gun. Under the mental onslaught of the Solar-Brain, Magnus is compelled to pick up the gun, and turn it on himself. Only Lead is able to resist the mental compulsion of the Solar-Brain, enough to cause the gun to backfire. With the Metal Men destroyed, Magnus is forced to take on the Solar-Brain alone. Magnus leads the Solar-Brain towards his ship, where he quickly activates the Chain Reaction. As the Solar-Brain steps into the arc, it is destroyed. Magnus, en route back to Earth, begins the work to rebuild the Metal Men.