This is an odd one-shot comic book in which Peter Parker (now married to Mary Jane) is having nightmares about the Joker. And Bruce Wayne is having nightmares of Carnage, one of Spidey's foes. Their origins are paralleled-Peter about the death of his Uncle by a hoodlum, Bruce about the death of his parents by one. Spiderman is asked to come to Ravencroft Institute, where Carnage is being held. He nearly escapes but is subdued. Meanwhile, Bruce has a run-in with The Joker, who bites him in the neck. The Joker is captured and taken to Ravencroft, where scientists have an idea to implant a chip in their brains, to control their villainous behavior. It doesn't quite work out as planned and it's up to the two heroes to get things under control.
It's interesting to see these two characters together and it's presented as if they've always lived in the same "universe" together, rather than it being a cross-over between different worlds/dimensions.