In season 6, episode 2 of Doctor Who, (Day of the Moon), we see a character that suddenly appears but is never seen again in this episode.
Amy briefly saw a woman with an eye patch looking through a small window in a door. This woman looked off-camera and said, "No, I think she's just dreaming." The window then disappeared and the incident seemed to be forgotten and was never referred to again. What was happening there?
Moderator note: This is a questions and answers site, not a discussion board. If you want to add just a bit of information, consider editing an existing answer. If you offer interpretations, please indicate what clues they are based on. Answers are supposed to keep making sense in the future, so avoid expressions like “today's episode”.