It's not what it sounds like. Published in 1927, this odd little novelette is about a lonely, mid-30's spinster whose mother has just died. Alone in the house (except for the servants), she remembers that as a child, she had an imaginary friend, Clarissa, whom she had to give up when a new governess shamed Agatha about it. Now, friendless and alone, she tries to rekindle Clarissa. She's so successful that other people begin to be able to see her...and things get weirder from there. A nice exploration of loneliness, desperation, and the restrictions of the era. Has the feel of a gothic ghost story, without all the hand-wringing and hysteria. Short enough to read in one evening.