A ruminative, intellectual story about a young girl whose new adult friend turns out to be a demon trying to trick her into despair and suicide. Kate's parents are divorced, and now she's being forced to leave behind her perfect life in N.Y.C. to live in the country. Luckily, so she thinks, a man in the library has shown her how to ""subtract"" (i.e., suppress and deny) feelings and things; later, in the new house, another somehow-familiar ""Nat Worthy"" presents himself and subtly keeps Kate's attention focused on the past and a quixotic attempt to reunite her family. Interspersed transcripts reveal that Worthy is actually a proud devil, Jaster, assigned to rain Kate. Jaster bumbles, however, accidentally providing Kate with the clues to her self-administered redemption. Kate is presented as a 12-year-old genius, but her musings and urges are rambling and confused; nonetheless, she frees herself through her own efforts, without help from adults, least of all her self-absorbed parents. The author, appropriately, pays homage to C.S. Lewis, but this lacks both The Screwtape Letters' profound humor and the moral insight of Babbitt's The Devil's Storybook. Silsbee steers Kate through situations and mental states that are all-too-familiar to many young people, although his attempt to add a cosmic level roils the waters.