Through six turbulent months of 1934, 17-year-old Cassandra Mortmain keeps a journal, filling three notebooks with sharply funny yet poignant entries about her home, a ruined Suffolk castle, and her eccentric and penniless family. By the time the last diary shuts, there have been great changes in the Mortmain household, not the least of which is that Cassandra is deeply, hopelessly, in love.