In "The Sign of Four", Mary Morstan (later to marry Dr. Watson) states "... My father was an officer in an Indian regiment, who sent me home when I was quite a child. My mother was dead, and I had no relative in England. ..." In "The Five Orange Pips", Dr. Watson explains "... My wife was on a visit to her mother's, and for a few days I was a dweller once more in my old quarters at Baker-street. ..." Unless Mary Watson was on an extended visit to her mother's grave, this doesn't make sense.