The Story: "The Reverse-Spells of Zatanna's Magic!" by Gerry Conway, Dick Dillin, and Frank McLaughlin. The JLA has a meeting where they decide to add Zatanna to the team!
Zatanna--bearing a new costume--shows up to tell the astonished heroes she doesn't want to join! They ask Zee if something is wrong, but she says no. She doesn't want anyone's help or interference--especially not Green Lantern's! Hmm...
The team, stunned, breaks up and heads home ("What about Adam Strange?" Flash is heard muttering), but The Atom, on Monitor Duty, thinks something is fishy.
Just as Atom calls Batman to ask him for help, Green Lantern materializes in the satellite and zaps Atom unconscious! Of course, this is not the Green Lantern. This faux-GL does some research to find out more about this power ring he has, but is frustrated to find out he can't locate the power battery to charge it.
He mentions something about casting spells, and needing to neutralize the rest of the JLA, "just like I did to my old foe, Zatanna."
Meanwhile, we find Zatanna fighting a horde of demons in an alternate dimension. She is knocked out by one of them on the steps of a castle. We get to peer into the castle, where we find Green Lantern, stiff as a statue covered in cobwebs!
Batman does some investigating, and after talking to Zee's father Zatara, and figures out Zatanna's odd behavior was a ruse, and she was leaving some sort of clue for the JLAers to figure out.
The Atom wakes up, tells them what happened, and they follow the Fake Lantern's flight-path...to the mysterious city of Angkor Wat. Once there, Red Tornado is zapped by the evil Green Lantern. He then blasts the others.
Zatanna is helped out by a cavalry of soliders from different eras she called up with a spell. Once her gag is removed, she casts a spell freeing the real Lantern.
We then see that the evil GL is really The Warlock of Ys, who apparently cast a slow-burning spell that had him switching bodies with Lantern. He then put a spell on Zatanna, preventing her from directly warning anyone of Ys' plan, or even to use her backward spells. But he didn't realize Zee had freed Lantern, and they easily knock him out with a big green fist.
Epilogue: The case solved, the JLA asks again if Zatanna wants to join the JLA...which of course she does!
Roll Call: Superman, Batman, Wonder Woman, Aquaman, Flash, Green Lantern, Green Arrow, Atom, Hawkman, Black Canary, Elongated Man, Red Tornado, Hawkgirl, and new member Zatanna!
Notable Moments: The Warlock of Ys apparently set this spell when he first met GL, in Green Lantern #42. Since this was before DC started fudging with the chronological dates of the characters, that means that Ys' spell took twelve years to fully kick in. Now that's patience.
Zatanna was a fine addition to the JLA. The added female quotient was good, and her powers nicely balanced out the rest of the team, as did her relative youth. She would "jump ahead" a lot of older members, in that she would participate in a lot of future JLA stories, many more than some of the others.
I was lucky enough to meet both Rich Buckler and Frank McLaughlin at the New York Comic Con a few weeks ago, so I took the opportunity to get them to John Hancock this cover, one of my all-time favorites from the book: