Everybody raise your hands! Although I'm generally a big fan of Herb Trimpe, this is a pretty mediocre cover. Shouldn't Betty have some sort of look of dismay and concern, rather than a happy, almost adoring gaze at something off-camera? The cover is at best an homage to (at worst a swipe from) Fantastic Four #33, complete down to the guy at the bottom right with two horns.
And the story itself is a swipe from virtually every wedding in the DC and Marvel Silver Ages. It opens with the Leader reading a newspaper about Bruce Banner and Betty Ross' impending nuptials.
FF Annual #3 opened with Dr Doom reading a newspaper about Reed and Sue's impending nuptials.
The Leader decides to disrupt the wedding; Dr Doom disrupted the FF's wedding, the Reverse-Flash disrupted the Flash's wedding, and the Ringmaster and his Circus of Crime disrupted the wedding of Hank Pym and Jan. The Leader observes Bruce and Betty as they share a romantic rowboat on a lake. He is all set to kill them with one push of a button, when he has an evil genius moment:
What these evil genius moments amount to is a "get out of a plot point free card" for writers of comics stories. It allows the writer to put the hero in a much more difficult situation, because he knows that the villain will not do the obvious thing and immediately put a couple of bullets into the hero's skull. These moments are amusing because even back as teenagers we could see that this was the moment the villain could have succeeded, if only he hadn't insisted that it was too easy, too painless.
At any rate, nobody can accuse the Leader of lacking imagination. He decides that the best revenge would be to have the Hulk return (apparently Banner had found a way to prevent his bestial side from emerging at this point) and kill his bride on their wedding day. But he needs an ally from among the Hulk's enemies, so we get a brief rundown of the Sandman, Namor, the Mandarin, Maximus of the Inhumans, the Space Parasite, and the Rhino, whom he selects.
The Rhino had previously fought the Hulk in IH #104, and nearly died in a fire. In fact, the Hulk thought he had died, but villains seldom died for good in the Marvel Silver Age. He's still in a coma, so the Leader kidnaps him with a giant android, and then revives him with mental blasts. He augments the Rhino's powers and returns his horned suit.
They travel surreptitiously to the house of General Ross, where the wedding is to take place. A gamma-ray beam weapon transforms Banner:
We get another "this is where the plan went off the rails" moment here:
If you think about it, the idea of bringing the Rhino along never made any sense in the first place. If the goal was to use the beam to make the Hulk savage enough to kill Betty, the Rhino is useless. At any rate, you can probably guess the ending of the story from here. The Rhino gets in the way of the ray himself, and in anger turns on the Leader. The Leader tries to escape, but his craft is unstable with the Rhino hanging on and it crashes, apparently killing them both. (Hah!)
But the battle was not without its casualties on the good side:
Now a reasonable person might ask why you're saying this to the fiancee of the man you're talking about killing, especially since it seems clear that Banner himself was completely blameless for what happened. We know Talbot's trying to get Betty for himself, but it hardly seems likely to soften her heart towards him.
This story is unique in the Silver Age in that it is the only one I can find where a superhero (Hulk is arguably a hero) and his girlfriend were prevented from marrying by the villains. Betty and Bruce did marry eventually, but it was about 16 years later.
Trimpe's artwork is terrific aside from that rather dull cover, embellished marvelously (as the Groovy Agent notes in the comments) by Sal Buscema's inks. The story is just okay; although I am a big fan of Roy Thomas, this is not one of his better efforts.