The Field Guide (Spiderwick Chronicles Series #1)

When their great-aunt Lucinda Spiderwick is sent off to an asylum, the Grace kids -- twins Jared and Simon and their older sister, Mallory -- move into her creepy old mansion with their mother. Strange goings-on lead them to an old book filled with pictures of fanstastic creatures. It holds clues to recent odd events, and the key to an even bigger mystery: the disappearance of the children's great-uncle Arthur Spiderwick generations before....