10. Who Is Holiday? - The Long Halloween
Although Jeph Loeb and Tim Sale would go on to helm two further Batman stories afterwards, The Long Halloween represents the pinnacle of their time together on the Caped Crusader.
Set during the early years of Batman's vigilante career, The Long Halloween is to many the definitive Batman mystery. It revolves around a war between the Falcone and Maroni crime families, the burgeoning days of Batman's rogues gallery, and of course the Holiday Killings. Various figures are murdered on the different holidays of the year; meanwhile, Batman, Commissioner Gordon and Harvey Dent forge a formidable partnership in a bid to take down the mob for good.
It's legendary stuff, especially seeing how much the comic has to juggle. Still, the mystery surrounding the murderer specifically - known to the general public as Holiday - is fantastic. Even at the end, when everyone believes Alberto Falcone to be the guilty party, Loeb and Sale pull a complete 180 and reveal that Gilda Dent - Harvey's wife - was behind several of the murders.
The final panel shows her uttering Harv's trademark slogan - "I believe in Harvey Dent" - in a haunting confirmation that Gotham's madness touches everyone.