The plot of "The Tell-Tale Heart" is fairly simple: the narrator develops an unnatural hatred of the eye of the old man with whom he shares his house; he concocts a plan to kill the old man, which he does; after he has cut up the body and hidden it under the floorboards of his house, the police come. They suspect nothing, but the narrator, consumed with the consciousness of his murder, hears the heart of the old man beating, which drives him in a final frenzy to confess to his crime.
What is “going on” in the story is a little different. The narrator tells the story of the murder presumably to demonstrate his sanity. The elaborate slowness of his pursuit of the old man, the dread he is able to engender in him, how cleverly he hides the body—all this is meant to be seen as proof of intelligence, not madness. Yet the narrator is clearly crazy. The “vulture eye” of the man perhaps triggered the murder, but what motivates the narrator is a more general sense of paranoia and a morbid fixation on the difference between life and death. His hearing of the heartbeat of the dead man is an expression of that paranoia, of course, but also a painful reminder that his own heart is still beating. The old man’s murder can be seen as an outward manifestation of the inward mental state of the narrator: as he says when the old man, alone in the dark, lets out a groan of terror: “I knew what the old man felt, and pitied him, although I chuckled at heart.”