The Story: "The Creature in the Velvet Cage!" by Len Wein, Dick Dillin, and Dick Giordano. We hit the ground running, as the first page features the JLA and the JSA in a good old-fashioned superhero donnybrook with some goofily-dressed bad guys, when the Sandman gets an alarm in his car(The SandMobile?) and takes off without a word to his comrades.
They follow him back to his home, where they find Wesley Dodds in a secret room(The SandCave?) that features a giant class bubble, shattered into a thousand pieces. Dodds tells them that the person in the bubble was his former sidekick, Sandy!
He tells them that, years ago, during an experiment, something went wrong and Sandy was transformed into a giant, malevolent crystalized sand creature, who luckily passes out from the stress before he got a chance to attack The Sandman.
The Sandman then made the decision to imprison Sandy until he could find a way to reverse what had happened, and it stayed that way for years...until today!
The two teams spread out to find Sandy, and each time they find him, he manages to turn into sand and disappear. He's finally stopped by the Sandman himself, who bets that somewhere deep inside this creature is still his boy partner.
This calms him down long enough for him to explain that a small earthquake had cracked his glass bubble, and Sandy was able to explain that in his new form he could sense a bigger disaster looming and he tried to stop it. Sandman can't understand, since he assumed Sandy was a mindless monster:
...turns out Sandy had been imprisoned all these years, trapped in both the prison of his body and the bubble, unable to ask for help because of the Sandman's knockout gas!
This sends Sandman into paralyzing despair, knowing his misjudgment has taken away years of his friend's life.
Roll Call: Superman, Batman, Green Lantern, Elongated Man
Notable Moments: I always found this story tragic, which is obviously what Wein intended. Had Sandman, you know, asked someone for help, he could've avoided all this. It's not like he didn't know world-class scientists, galaxy-hopping explorers, and powerful sorcerers.
This issue also features a two-page piece called "The Freedom Train", about the train that in 1947 carried some of America's most historic documents(the opening panel has Superman, Batman, Green Lantern, and, surprisingly, Aquaman(and a yellow-gloved one at that!) watching the train go by).
It also features the JSA in "The Case of the Patriotic Crimes"(from All-Star Comics #41), and "The Cavern of the Deadly Spheres!" from JLA #16.
This is the only one-part JLA/JSA cross-over!