When Mallory and Jared attempt to rescue Simon from goblins, they use a magical stone which enables them to see things that are normally invisible.

Sequel to: The field guide. Book 2 of the chronicles.

Letter from Holly Black -- Letter from Grace kids -- Map of the Spiderwick Estate -- More than a cat goes missing -- Several things are taken, including a test -- Mallory finally gets to put her rapier to good use -- Jared and Mallory find many things, but not what they are looking for -- Fate of the missing cat is discovered -- Jared is forced to make a difficult choice -- Simon outdoes himself and finds an extraordinary new pet.