At the heart of the graphic novel was the idea that any man could be driven mad by going through one bad day. The comic book saw the Joker test that very theory on Commissioner Gordon, by torturing him with shocking footage of his daughter Barbara Gordon held prisoner. On television, Gotham decided to have Jeremiah explore the theory -- which he got from his twin brother -- by subjecting Bruce Wayne directly to it, instead of Gordon. This makes a lot of sense for the series, which is bringing Bruce ever closer to the mantle of the Bat.
Where in the comic book, Gordon was forced to see pictures of his daughter, whom he loves, Bruce sees the videos of the only person he truly loves: his butler and father figure, Alfred Pennyworth. In a warehouse, Bruce sees brutal projections of Alfred being tortured, and he can do nothing but watch in panic. However, one big difference in the series was the addition of the Scarecrow, who pumped the warehouse full of his fear toxin. Jeremiah hoped that the combination of the poison and the trauma of seeing Alfred get hurt would be enough to drive Bruce over the edge -- and it almost did. Were it not for the intervention of Selina Kyle, Bruce might have snapped. Like Gordon, who was saved by Batman in the comic book, Bruce managed to disprove the theory.
Later in the episode, Bruce and Selina find themselves at Wayne Manor, as the two recover from the ordeal they just went through. And it's there that Bruce echoes one of the main themes of The Killing Joke. The comic book ended with a moment that was unheard of, as both Batman and the Joker shared a laugh over a joke. It was a simple ending, but one that showed how truly similar the two were. It was even meant to make us wonder how stable Batman was, and if he was just as damaged and maniacal as the Clown Prince of Crime. In "One Bad Day," Bruce and Jeremiah may not share a laugh, but Bruce's torture was enough to make him wonder if he was just like Jeremiah. He wonders if, perhaps, the murder of his parents drove him insane.
It's undoubtedly a terrifying way to look at the origin story of Batman, but it's always been one that has been hiding beneath the surface. Fans have known for years how damaged Bruce Wayne is, and how his crusade comes above anything else. The question of Batman's sanity has been brought up before, but perhaps never this early in his crime-fighting career. Bruce's realization means that he has become self-aware, and that can only mean that this will make him a better hero.
Because yes, Bruce Wayne is a hero -- there is no denying that fact. As for Jeremiah/Joker, he will always be a villain. There will always be that distinct difference between the two, a clear line that separates one from the other. More than anything, Gotham found a brilliant way to demonstrate how its version of the Joker is the other side to Bruce's Batman coin.
Airing Thursdays at 8 p.m. ET/PT on Fox, Gotham stars Ben McKenzie as James Gordon, Donal Logue as Harvey Bullock, David Mazouz as Bruce Wayne, Robin Lord Taylor as Penguin, Camren Bicondova as Selina Kyle, Erin Richards as Barbara Kean and Sean Pertwee as Alfred Pennyworth.