With Gordon's help, Peter sorted out the timeline.
Two months earlier, Joker had created the Titan Virus. When he got his hands on it, he realized a perfect opportunity had arrived.
So he pretended that he wanted to use the virus to create more villains. He even broke into Arkham Asylum, only to be subdued in the end.
It looked like yet another evil plan by Joker to destroy Gotham, but his sword dance had been aimed at someone else. All of it had merely been a facade.
In private, Joker used the Joker Virus in his own blood to infect five ordinary people, confirming that the virus would give the infected some of Joker's traits.
A month and a half earlier, Batman had stumbled across ordinary people infected with the Joker Virus. At the time, he had not fully anticipated Joker's plan and was still occupied with the Titan Virus. He had merely sent those infected civilians to a base.
A month earlier, Joker had transfused Batman with his blood. The two fought their final battle at Gotham Grand Theater, and Joker ultimately died when the Titan Virus erupted and he failed to receive the antidote in time.
Three weeks earlier, Batman entered Battleworld, met Peter, and had even been willing to pay an enormous price to bring Peter to his universe.
Two weeks earlier, Peter began investigating the city. He discovered signs that Scarecrow had buried Fear Gas around the city to cause accidents, formulated a plan, and began carrying it out. The first step had been kidnapping Black Mask.
A week earlier, Scarecrow and Penguin struck some kind of deal. Penguin provided Scarecrow with weapons and military transport for his Fear Gas destruction plan.
A few days earlier, Gordon discovered the base Batman was using to detain