Sumac Lottery is nine years old and the self-proclaimed good girl of her very large, extremely unruly family. And what a family the Lotterys are: four parents, children both adopted and biological, and a menagerie of pets, all living and learning together in a sprawling house called Camelottery. Then one day, the news breaks that one of their grandfathers is suffering from dementia and will be coming to live with them. And not just any grandfather; the long dormant Grumps, who fell out with his son so long ago that he hasn't been part of any of their lives. Suddenly, everything changes.