midnight
I believe I know her whole story . But the mystery is inexplicable ! I would take down these walls if I thought I could get at the secret . '' Long past midnight we sat and talked it all over ; and racked our brains in vain to invent any theory to account for the appearance of the letters on that cellar stairway . My uncle 's tender interest in the poor dead Esther was fast being overshadowed by the perplexing mystery . A few days after this , Mary the cook found another of the letters when she first went down-stairs in the morning , and Robert placed it by my uncle 's plate , with the rest of his mail . It was the strangest one of all , for there was not a word of writing in it that could be read .