What is the content of the mysterious notes and who is writing them?

Miranda has been receiving notes from an unknown source and this novel is written as though Miranda is speaking to this mysterious person. The content of the notes is unknown at this point, but Miranda mentions that the author of the notes has asked for Miranda to mention the location of a spare key to her apartment and the date on which her mother will appear on The $20,000 Pyramid. This suggests knowledge of the future, something it will be important for the reader to remember as the plot continues to develop.