How does the author create the effect surprise in the cask of amontillado

Montresor leads Fortunado deep into the family burial crypt promising him some delicious wine, but it is a trick. When they are so deep in the cave that no one can hear, instead of giving Fortunado wine, Montresor chains him to the wall and builds up a false wall around him with stones and mortar and leaves him there to die. He gets his revenge.