"When Arthur and Rose Trout were little, they were the heroes of Roar, an imaginary land they created together. Roar was full of their favorite things--ninja-wizards, mermaids, unicorns, dragons, and fantastic places to explore and play--but it was also full of things that sent shivers down their spines. Now that they're eleven, Rose would rather play on her phone than play games with Arthur, who can't resist teasing her every change he gets, and...