The narrator begins to think about killing the old man he lives with. Gradually he becomes obsessed with his desire to kill him although he doesn't really understand why he wants to do so. He keeps spying on the old man while he is asleep. The reader knows that sooner or later the narrator, who is obviously a madman, is going to commit a horrible murder. The suspense keeps building. The reader knows that there is going to be a murder committed but does not know when or how it will occur. Even the old man seems to know his life is in danger. He lies there in fear each night but seems paralyzed and unable to take any action to save himself.
When I had waited a long time, very patiently, without hearing him lie down, I resolved to open a little—a very, very little crevice in the lantern. So I opened it—you cannot imagine how stealthily, stealthily—until, at length a simple dim ray, like the thread of the spider, shot from out the crevice and fell full upon the vulture eye.
The narrator begins to hear what he takes to be the sound of the old man's heart beating furiously because of his intense fear. This heartbeat will continue to be a strong effect throughout the rest of the story and will give the story its title.
But even yet I refrained and kept still. I scarcely breathed. I held the lantern motionless. I tried how steadily I could maintain the ray upon the eye. Meantime the hellish tattoo of the heart increased.
And then, finally, the narrator acts.
The old man's hour had come! With a loud yell, I threw open the lantern and leaped into the room. He shrieked once—once only. In an instant I dragged him to the floor, and pulled the heavy bed over him.
For a brief interval the narrator thinks he has committed the perfect crime. He dismembers the body and hides it under the floor. But the old man's single shriek and the murderer's "loud yell" have alarmed the neighbors. The police show up at four o'clock in the morning, just after the narrator has put everything back in order. The narrator behaves with complete composure, and it appears that he is going to get away with the murder. After all, everything looks perfectly normal. But then he begins to hear that beating heart again. He believes it is his victim's heartbeat, even though he has cut off the old man's head as well as his arms and legs. The heartbeat continues to drum louder and louder in his ears. Evidently it is his own heart beating with fear of being exposed as a murderer.
Yet the sound increased—and what could I do? It was a low, dull, quick sound—much such a sound as a watch makes when enveloped in cotton. I gasped for breath—and yet the officers heard it not. I talked more quickly—more vehemently; but the noise steadily increased.
The sound is so obvious to the narrator that he believes the policemen must also be well aware of it. If so, why do they say nothing about it? Why don't they seem suspicious? The narrator assumes they are playing cat-and-mouse with him. They are only waiting for that tell-tale heart to make him break down and confess. And finally he does so.
“Villains!” I shrieked, “dissemble no more! I admit the deed!—tear up the planks! here, here!—It is the beating of his hideous heart!”
He must be completely insane to believe that the old man's heart could still be beating after he had murdered him and cut his body into pieces. There has been a rising feeling of suspense since the beginning of the story. The tension increased up to the time of the murder. Then it began to increase even further when the police arrived. The narrator was not in any danger before the arrival of the police. The murder only made the tension greater because it brought the forces of the law. The narrator's exposure illustrates the thesis of Poe's story, which can be stated in the words used by Hamlet in Shakespeare's play:
For murder, though it have no tongue, will speak
With most miraculous organ
Macbeth expresses the same idea in another Shakespeare play:
It will have blood: they say blood will have blood.
Stones have been known to move and trees to speak;
Augures and understood relations have
By maggot pies and choughs and rooks brought forth
The secret'st man of blood.