Goosebumps Most Wanted: #9 Here Comes the Shaggedy

Kelli and Shawn move to another state, right next to a giant swamp that their scientist father can study. Legend has it that an ancient beast named Shaggedy lives far below the surface of the swamp.
Kelli and Shawn Anderson are not excited about having to move to another Stateespecially because their new home is directly next to a giant swamp. But their dad is a scientist and he's going down there to study the local flora and fauna. Unfortunately for Kelli and Shawn, there seem to be some very strange creatures that live around their house. They keep hearing about the legend of the Shaggedy, an ancient beast that lives far below the surface of the swamp and can cause a whole lot of damage. Can Kelli and Shawn convince their dad to move back home before it is too late?