The opening sentence establishes a revenge plot, and the narrator asserts that he must "punish with impunity" for the unnamed wrong done to him. The tone is thus established from the first paragraph as dark and vindictive, leading to initial feelings of suspense.
Poe also crafts an unreliable narrator to further the suspense. What exactly has Fortunato done to Montresor? What are these "injuries" the narrator has "borne" and which are so severe that Fortunato deserves to die for them? We never know, but we do know that the narrator is so deceitful that he is confident "that neither by word nor deed [has he] given Fortunato cause to doubt [his] good will." This narrator with an unnamed grudge, who is able to lie so effectively that his victim never suspects him, certainly furthers the story's suspense.
The murder plot begins in a suspenseful and ominous setting:
It was about dusk, one evening during the supreme madness of the carnival season, that I encountered my friend.
Night is falling....
(The entire section contains 3 answers and 1117 words.)