The book is based on the sense of sight as the other books are based on scent, sound, and taste. It acts as the continued part of This Book Is Not Good For You, starting just after Cass eats the magic "Time-Travel" chocolate and falls into a coma, searching for her ancestor, the Jester, to find out what the Secret of immortality is, as she recently became the new Secret-Keeper of the Terces Society. Meanwhile, Max-Ernest tries to save Cass with a special monocle, as the book centers around the sense of sight.