In the conclusion of the short story 'The Tell-Tale Heart' by Edgar Allen Poe, the murderer/narrator totally loses it - and gives the game away all by himself. Having murdered and dismembered the old man and disposed of all traces of him under the floorboards, he goes through all the painstaking interviews, questions and enquiries of the interrogating detectives without a hitch. As Poe builds the suspense and tension to fever pitch, the narrator does not think he can bear a minute more of keeping up appearances and imagines the victim's heart giving the game away under the floor by ticking louder and louder. In the end, it is a game of 'mind over matter' of his own choosing that lets him down at the conclusion of an almost 'perfect murder.' Guilt and fear of discovery bring his mental defences crashing down in conclusion.
The main conclusion of Poe's short story, "The Tell-Tale Heart" is that the narrator is indeed insane. In the opening paragraphs of the story, the narrator goes out of his way to ensure the reader that he is not mad. He then goes on to tell that the weird eye of the old man for whom he cares has caused him to want to kill him. He goes through with the murder and chops up his body into little pieces. He then proceeds to hide the pieces underneath the floorboards. As the days tick on, the man believes he has gotten away with the perfect murder. When the investigators come to question the man, he answers their questions with no problems. They prolong their stay, and the man becomes convinced that he can hear the old man's heart ticking. The ticking becomes progressively louder, until finally, the man breaks down and tells the investigators what he has done. He is then arrested and taken away.