The Mechan Monster is a robotic monster from another dimension, the Metal Men faced it as the first of three task for King Dymond in lieu of a way to restore Doc Magnus back to life. Doc Magnus is working on yet another wondrous invention, a dimension monitor which will allow travel to other dimensions, suddenly the main electrodyne blows and the Doc falls to the fall, the Metal Men rush over but Doc Magnus is dead.
Altered Metal Men Sober minutes pass by but the Metal Men cannot revive the Doc, Tina decides that they must use the dimension monitor to try to find a way to save the Doc. The ingenious robots fix the machine and a door opens to another dimension. The Metal Men carry the Doc in a sarcophagus through the portal to a strange land. Once through the first thing the group notice is that changes have occurred to some of the groups, Gold has become Copper and Mercury has turned green. Gold also discovers that he has lost the power of speech at which Mercury declares himself leader although he is brittle on this strange world. Suddenly a meteor shower hits so Iron creates a shield but is stunned to find that he is now a soft metal and the storm pierces him, Tin forms a shield and discover that he and Nameless have become hard metals. a wind picks up and lead floats away, he has become a super light metal. Copper pulls him back to earth and the group move forward. Platinum steps into a puddle and discovers that she is flammable when she steps into a puddle.
Eventually they reach civilization and they approach the king, who announces they can restore Doc but they must perform three tasks Copper who cannot speak hears that they plan to trick the Metal Men but cannot convey this. Their first task is to defeat the Mechan Monster, so they set off to tackle the beast.
Once they track it down the monster attacks Mercury tries to form a plan to stop it but they are getting beaten, so he calls on the Metal Men to form a gun which they do, however the Mechan Monster smashes them apart with ease. The try different tactics, first lead and Iron reflect the sun at the monster melting and arm, Tin and Nameless ram it shattering it more and Copper acts as a conductor to a lightning bolt which blasts it apart, once done mercury finishes it off. They then return the smashed robot to the king who gives them the second task to perform which is to find some fabulous lost treasure.
The first obstacle is a ravine so Tin forms a bridge for them to cross, then they go through a dark ravine but Platinum glows showing them the way. Next they reach a huge wood, so lead forms a balloon and Iron a basket so they can float over. They then have to cross a solid rainbow where they reach an X on the ground, Tin digs and digs but finds nothing. Copper draws an axe in the sand, so Tin forms an axe and Nameless swings him at the tree next to the X. All of a sudden a box falls out of the wood, the metal Men take it back to the king who announces it to be the rarest thing in their world, although it looks like clay bricks to the Metal Men. The last task is to rescue the kings daughter from the mad maze, so of they set although Copper knows that King Dymond means to trick them. Inside the the maze the Metal Men are bewildered by many maddening optical illusions and are completely confused. Copper though shuts his eyes and moves forward leaving a trail of wire behind him. At last he manages to find the exit and the others follow the wire he has left behind to escape also. Tina finds a perfume bottle will allows them to find the princess in a garden of giant flowers and take her to the king along with her boyfriend to get the life elixir for the Doc.
As Copper suspected the King Dymond has no elixir and Tina flips in her grief she starts crying tears of fire and her tears fall on the perfume bottle which causes a strange chemical reaction to occur and as Tina bends over to kiss the Doc goodbye, he suddenly opens his eyes. The Metal Men forgive the king who is sorry for what he has done.