Author's Note:
To avoid any confusion, I'm replacing chapter one, which was basically an almost verbatim retelling of what happened in the comic, with this placeholder chapter.
These characters and worlds are property of DC Comics, Warner Brothers, and whoever has rights to them.
Main continuity Jason Todd, while on Earth 3, is rescued from the Crime Society by a version of the Joker who claims he's a hero and wants to help fight crime. Since Jason was killed by the Joker, he doesn't believe the clown in the least, and when he discovers that the clown has followed him, Dona, and Kyle Rayner on their multiverse hopping search for Ray Palmer, he becomes increasingly frustrated.
Finally, Jason can't take it anymore and throws the clown on the ground after he refuses to leave him alone.
The clown, not really sure why everyone is upset by his mere presence, finally asks, to which Jason angrily replies, "on the Earth I'm from, the Joker murdered me!"
Jokester is taken aback upon hearing this, replying, "oh...I'm...sorry?"
Jason then continues to glare at him angrily.
"...but I really am called the Jokester."
The two are ready to go at each other when they are interrupted by more doubles from whatever Earth they were transferred to.
Jason continues to learn about the multiverse and the consequences of different outcomes of his actions, all while keeping one eye trained on the Joker look-a-like.
Eventually, they arrive on a hostile alien planet and are nearly obliterated. Jason is caught in the line of fire, but the Jokester, once he hears that one of the monitors killed Joker's Daughter, his daughter, jumps in front of him at the last minute, taking the brunt of the blast and supposedly killing himself in the process.
...
"You're not going to kill anyone as long as I-" Jokester yelled as he leaped between Jason and the laser gun.
Jason winced as the blast was fired. It went through the clown's body, shattering his bones, but when the smoke cleared, he and his group were okay and had just enough time to escape.
As Bob powered up, Jason, from the safety of the energy bubble briefly watched the man who had saved his life by giving his own. In that moment, Jason realized he was wrong. Whoever this man was, maybe he wasn't so bad, after all?
Jason stared at the pale faced comedian; he had all of the Joker's scars and hideous markings, including that awful unsettling grin, but that man was definitely not the Joker. The tiniest wave of regret washed over his heart as he was transported to yet another Earth to continue the search for Ray Palmer.