Some TMNT stuff really isn't for little kids.
The team behind the smash-hit crossover series is back to reunite the Dark Knight and the Heroes in a Half-Shell. When Donatello goes looking for a new mentor to help him improve his fighting skills, he opens a doorway to another reality, hoping to summon the Turtles’ one-time ally, Batman. But instead, he gets sent to Gotham City and someone else comes through the open portal—Bane! Suddenly, there’s a new gang boss in New York and he’s out to unite all the other bad guys under him. Can Donnie get back in time and bring Batman with him to help his brothers before Bane causes irreparable destruction?
A panicking man races out of a subway, desperately calling for the police because of a "demon" he saw. He tries to explain that it didn't sound human, and that it said he should run because it was saving him. It's revealed that the frightening figure was actually Michelangelo, and that the Turtles passed the man on flying skateboard-like devices.
In a subway car, Karai battles the Elite Guard for dominance of the Foot Clan, and when she's knocked out of the car, Michelangelo catches her. She angrily dismisses him, saying that she doesn't need his help, and that the Turtles started the whole mess by having Shredder thrown in prison. Meanwhile, Raphael and Leonardo attack the Elite Guard and knock them out into the subway tunnel, where Donatello is waiting.
Donatello attaches a device to the third rail and charges up a taser rifle, which he fires at the Elites. But he misses, and they knock it from his hands. As he fights them, the Elite leader sneers that Donatello is not a true ninja, that he tries to hide his weakness behind his machines, and even that Splinter must have contempt for him. He knocks Donatello to the ground and prepares to spear him, but is interrupted by Michelangelo. As his brothers rush in, the Elite refers to Donatello as the "runt of your litter" and tries to kill him again, but he's saved by a punch from Raphael. Though the Turtles are triumphant, Donatello is clearly shaken and upset.
In Gotham city, a ninja scales up to a rooftop and enters a secure facility. He reveals that the League of Assassins want to make "him" their new leader, and that they know of a Lazarus Pit hidden under Gotham. Suddenly Batman looms up behind him. He demands to know what is happening, and the ninja reveals that after Ra's al Ghul's defeat alongside Shredder, a faction of the League believes that he is too weak to lead them. Robin confirms that one of the cells at Arkham Asylum was torn open from the inside, and the two heroes head out into the night.
Back in the Turtles' world, Casey Jones is stitching up Donatello's injuries while his brothers each relax in his own way. While the others discuss how the splintered Foot Clan is after the Turtles, a clearly depressed Donatello leaves to speak to his father. He feels that he failed because he wasn't strong enough, and that he will always be the weakest of his brothers even if he is the smartest. Splinter tries to reassure him that nobody can be everything, but Donatello points out that Batman is a genius as well as a great martial artist. Still clearly troubled, he leaves the lair.
Back in Gotham, Batman and Robin race towards the pit and are attacked by the Ninja Man-Bats. Robin manages to get close to the Lazarus Pit, but discovers that they are too late: Bane is already in it, laughing maniacally.
Donatello arrives at Harold Lillja's lab and decides to use the teleporter to contact Batman. As he succeeds, a squad of Foot Clan ninjas, including the Elite Guard, appear in the lab around him and attack. In desperation, Donatello accidentally backs into the portal and appears in Batman's world, just as Bane also vanishes.
Back in the Turtles' world, Bane appears in front of the Foot Clan ninjas...