How has Montresor managed to empty his house of all his servants?
The setting of the story is during the carnival season. The narrator (Montresor) portrays himself as ultra savvy and states:
There were no attendants at home; they had absconded to make merry in honour of the time. I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned.
Thus, Montresor uses reverse psychology on his servants. He knows that if he tells them not to leave the house when he really wants them to, that they will disobey him because he has "leaked" the information that he will not be home to verify if they are there. In setting up this scenario, he provides himself with an alibi because the attendants will tell those who ask that their master was out of the house and will, of course, tell no one that they were not there in order to cover their disobedience. Additionally, Montresor is free to kill Fortunato with no witnesses.