A fourteen year-old girl, Nancy, receives an initiation about her extended family's ritual of fighting the massive crawdad that lives near their lake house. It is a piece of news that is so grim that children have tried to escape in the past, but Nancy takes interest in the upcoming battle and modifies her tennis racket so that it becomes a deadly weapon.
The family sails out on boats to wake up the crawdad and fight it. Nancy's weapon causes significant damage, but the Crawfather still captures and eats Madeleine, a young woman who is soon to be married. Her fiancé, who is not a part of the family, descends into grief as the family returns back home.
Nancy and Archie, another teenage family member, out in the middle of the night. They launch flaming arrows at the Crawfather and successfully kill it, which the family has been working together to do for years. However, the family is dismayed when they find out that the monster is dead, as fighting it has united them, given them a common cause, and strengthened their love for each other.