Answer:
The passage from "The Cask of Amontillado":
"Pass your hand, 'I said, 'over the wall; you cannot help feeling the nitre. Indeed it is very damp. Once more let me implore you to return. No? Then I must positively leave you. But I must first render you all the little attentions in my power."
reveals that C. He hopes Fortunato will prevent him from committing the planned murder.