A cat that is not a cat insists on being a girl's companion.When 12-year-old Nell and her older sister, Lulu, go to help Aunt Jerry with managing her inn, the mysterious feline that followed Nell home from an alley comes with them. Nell thinks of the protean, catlike creature as the Netherbeast. It is remarkably smelly-descriptions of its transformations involve awful odors and emanations of goo-and it's capable of inflicting terrible injury with its many claws and teeth. It adores Nell, who doesn't buy its sweet kitty disguise. The girls arrive to discover Aunt Jerry's Rose Cottage Bed & Breakfast literally falling apart. The formerly warm and welcoming guesthouse now harbors a furious rage: Plants in the garden die, shingles and bricks fly loose, and books come crashing down. Famous travel influencers have booked a stay, but things are neither rosy nor ready for guests. The cause of the house's disintegration turns out to be a tantrum that a former occupant, now a ghost in the basement rumpus room, is having. The Netherbeast is weirdly fascinating, and Nell is an appealing heroine. Awkward and shy, she thinks of herself as a moose, a label given her by a school bully, in comparison with her petite and accomplished sister, but her talents for solving mysteries and returning lost objects to their owners, along with the Netherbeast's supernatural capabilities, come in handy now. The characters read white. Black-and-white spot art adds a whimsical touch.Entertainingly page-turning. (Fiction. 8-12)