The narrator hates the eye and decides to do something to it, which was kill it
The narrator claims he has a "disease" which makes all his senses especially his hearing super sensitive. So he shares an event to prove he is not insane
"Three planks from the flooring of the chamber, and deposited all between the scantlings. I then replaced the boards so cleverly so cunningly, that no human eye -- not even his -- could have detected anything wrong. There was nothing to wash out -- no stain of any kind -- no blood-spot whatever"(Poe).
That direct quote from the text shows a rising action of how the narrator kills the "eye" and states that he left no possible way like blood for anyone to find out if he killed it.
The narrator tried to hide the fact he hid the eye under the floorboard by walking the police around the house and showing him there was nothing there
No doubt I now grew VERY pale; but I talked more fluently, and with a heightened voice. 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.
The quote to the side proves that. The narrator becomes more unwell and begins to get nervous because the police are there and he wants them to leave
The dialogue to the side shows that he has no idea how the voice got there but when it did it haunted the narrator day and night.
“It is impossible to say how first the idea entered my brain; but once conceived, it haunted me day and night.”
The narrator is overtaken with his insanity (hearing the heart) which reveals the characters guilt of killing the old man.
The narrator believes he is in the right, but once he retells the story, the guilt overcomes him.