Here's the standard synopsis:
A pained voice takes over the narration. The camera pulls back to reveal that a man in a suit has been watching the previous scene in a film:
It's a decent setup for a cartoon--not unlike the one in the Superman cartoon featuring a mad Indian scientist. Especially when you consider that it was an early 1960s cartoon. This may be the first description of the atrocities committed against Indians to ever appear in a cartoon.
Don Tay the dog
As one critic put it, Don Tay "is a fully clothed, well-dressed, thoroughly civilized, and educated man." Unfortunately, he looks like a racist caricature. He must be a mix of Indian and European blood, with perhaps some African blood thrown in. He has dark skin and a weird shock of white hair--but other than that, he resembles a dog. He's distinctly less human than the Euro-Americans he encounters. And his disguise, such as it is, is a black mask with a sombrero rim around his neck.
After Ferno steals some plans from the Institute of Science, we learn what Don Tay's scheme entails. Ferno is to dig a tunnel under Mount Smokum, an inactive volcano, to trigger an eruption. The lava will destroy a Mexican village. Presumably this will kill the Mexicans who enslaved his people as well as a bunch of innocents.
But Don Tay repents when he's surrounded by lava himself and Astro Boy saves him. He helps Astro Boy divert the lava and save the village. A lesson is learned: something about evil swallowing itself if left unchecked, literally as well as figuratively. And all's well that ends well.