Hey Arnold! The Movie is a novelization of the movie with the same title, written by Craig Bartlett and Maggie Groening.
Back cover description[]
When an evil corporate developer announces that he's buying and tearing down Arnold's neighborhood, Arnold is devastated. What's going to happen to the community he loves? Luckily, Arnold's grandfather remembers an event that might declare the neighborhood a historic district, so Arnold and his best friend, Gerald, team up to find out. With help from a mysterious caller named "Deep Voice," they attempt to track down a special historical document and uncover some surprising secrets along the way. Can they find the document before the bulldozers are called in? Find out in this captivating adventure!