With Romita taking over on the art chores two issues earlier, Amazing Spiderman began a new direction with #41. Peter begins to show increasing maturity. He purchases a small scooter to get around town. He also runs into Betty Brant and realizes he no longer has anything in common with her.
But of course, the supervillains keep coming. A new one is introduced in this issue: The Rhino. JJJ's son, the astronaut (last seen way back in ASM #1) was affected by some space spores during his last mission and the commies would love to get their hands on him. The Rhino is obviously working for them.
However, his battle with Spidey's rather dull; Peter just tires the Rhino out and wins by default. We don't learn his origin, or how he got that armor-plated skin and horn. Peter rescues John Jameson, but needless to say, his dad isn't satisfied that Spidey's not the real villain.
In ASM #42, we learn that the spores Jameson's son was exposed to have had a delayed effect, turning him to an ultra-strong and invincible superhero. In the meantime, Spiderman has apparently gone bad, robbing a bank in broad daylight. Hearing this JJJ decides that his son should be the one to bring in Spidey.
We also see Peter and Gwen starting to show sparks of interest for each other. Later, Spiderman has a short battle with JJJ's son before getting away. In a flashback, we learn that Peter had been in the bank when he realized that one of the money bags being carried by a gun was ticking. Hence his robbery was really just getting rid of a bomb.
When JJJ discovers this, he tries to call his son off the chase. But John Jameson is no longer rational; he's determined to defeat Spidey whether he robbed the bank or not. But Spidey defeats him by knocking him into an electrical dynamo which kills the spores and returns the astronaut to his normal self.
But the big shocker comes at the end of this story, as Mary Jane Watson, who has been hinted at for several years but never actually seen, finally makes her debut: