Part 3 of the 4-part "The Demon Laughs."  It was the team-up that never should have happened.  But now it has, and it's working wonderfully!  
Thanks to Ra's al Ghul, the Joker is about to put his master plan into action — the release of a Joker-gas bomb that will decimate the entire planet!  Of course, Batman will eventually stop the two — but that's only if Joker and Ra's don't kill each other first!