midnight
`` In the first place , as we both know , Miss Staples ' sudden attack of illness dated from a few days after this mysterious young woman crossed this threshold . `` Who she is , or whence she came , no one seems to have been clever enough to find out . `` She has come and gone from this house , alone , and at all hours , no one questioning her movements . `` She has taken full charge of the patient , from midnight until early morning , and each forenoon our patient seems to have grown alarmingly worse . We have both discovered the presence of arsenic , which has been administered to her . `` And now last , but by no means least , I have been observing this mysterious woman with keen scrutiny . I could stake my life upon it she wears a wig , that her complexion is a ` made-up ' one .