Maggin and Novick are joined by Frank McLaughlin on The Joker 7 (May/June 1976), which brings together Lex Luthor and the Joker for a really entertaining romp. Luthor had last been seen, in a very small role, in Justice League of America a couple of months before.
The story brings the two together at a movie theatre, where they are in disguise, watching film reels about their latest crimes. They go for a burger and hang out like old friends, and Luthor even helps the Joker escape when the police show up.
Sadly, the Joker does not exactly return the favour. Luthor has created a machine that will allow him to drain Green Lantern's will power, and Hal Jordan gets a cameo, completely unaware of the small part he plays in this adventure. The Joker screws up the plan, and his insanity, and Luthor's genius, wind up getting transferred into the other criminal.
Luthor goes on a crazy spree of aimless mayhem, while the Joker, now frighteningly rational, realizes that this transference will kill both of them if not reversed. He chases after Luthor, trying desperately to convince, and then to force, the other villain to go through another mind switch.
Seeing both of the characters acting so differently than they usually works really well, and the story is non-stop fun. At the end, the Joker manages to capture Luthor and force the mind switch again, even though this knocks both of them out, leaving them to be captured by a rookie cop on his first day.
There are some really nice touches in the epilogue as well. Luthor is tormented by the insights he had gained while insane, which he can no longer recall clearly. The Joker is revealed to have had a second hide out constructed under his cell in Arkham, where he can live at ease.
Luthor returns a couple months down the road in Superman.