Most significantly, that is it the Carnival season for Poe's setting gives rise tothe masquerade, recalling the Restoration Period of England in which the aristocracy disguised themselves and partied with those of the lower classes. Disguised, these people entertained their more prurient desires without reproach. Likewise, Montresor entertains his horrifying reprisals against Fortunatoby means of guise within the setting of the Carnival, a time of promiscuity, revelries, and debauchery.
Interestingly, however, Poe turns the setting of the masque into his classic arabesque that twists and subverts the plot as much of the guise is what actually is apparent, not what is hidden. For instance, Fortunato is disguised as a harlequin, or fool, when he really is foolish so he should not wear a disguise for what he already is. Another example occurs when Fortunato asks Montresor, "You are not of the masons?" and Montresor ironically replies, "Yes, yes" playing upon the double entendre of the word mason. In another masque Montresor, an Italian, presents the family coat of arms to Fortunato, but it is disguised by the motto of the royal arms of Scotland which indicates Montesor's deadly intentions.
Certainly Montesor, under the appearance of disguise gives Fortunato several hints of his intentions, but Fortunato is too crass to comprehend them. So, the real disguise in "The Cask of Amontillado" is the reality of Poe's horrific deed done during the time of the masque and the Carnival; a punishment with impunity.