Stevenson, ND. Scarlet Morning (Series) #1

"Book one"--Spine

"Viola and Wilmur have been waiting for their parents for fifteen boring years in the colorless town of Caveat. Their lives are a drudge of salt, trash, pirate stories, and what-ifs--until one very stormy night, when Captain Cadence Chase breaks down their door. They cut a deal with the captain: Chase can take their most prized possession, a mysterious book, but only if she takes them, too. After all, if their parents aren't coming, Viola and Wilmur might as well have a grand adventure to find them. Setting sail into the treacherous and beautiful world beyond Caveat, the two inseparable friends must uncover the facts behind legend--and the key to saving all of Dickerson's Sea from obliteration--before the truth tears them apart."--Publisher description

Ages 8-12