[2] A robot arrives at an inventor's secret lair and unloads a large amount of money it stole from a local bank into a vault.

The front page of the Daily Planet reports the robot's robbery right alongside an announcement for the display of fifty million dollars of the world's rarest gems at the local museum.

As Superman struggles to free himself from the power line's wires, the robot arrives at the lair, but instead of the jewels, the inventor finds Lois inside it.

When she refuses to tell the inventor what became the jewels at his demand, the latter prepares to lower her into a pot of molten metal in part of what appears to be an industrial foundry.

When Superman catches up with him, he manages to save Lois in the nick of time when the inventor threatens to drop her into the metal's pot, landing on a ledge below it.

The inventor, realizing that he has lost, attempts to commit suicide by jumping over the ledge he is standing on, but Superman seizes him and escapes from the lair with Lois in tow.

The Mechanical Monsters is the first story (from any medium) that features Clark Kent using a telephone booth to discard his street clothes and change into Superman.

[4][5][6] The short film was parodied on The Disney Afternoon series The Shnookums & Meat Funny Cartoon Show in the Pith Possum segment "Darkness on the Edge of Black" (part of episode 2).