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. Sumac has to give up her room to make the newcomer feel at home. She tries to be nice, but prickly Grumps clearly disapproves of how the Lotterys live: whole grains, strange vegetables, rescue pets, a multicultural household... He's worse than just tough to get along with -- Grumps has got to go! But can Sumac help him find a home where he belongs?