Anna can see that her grand-niece Minnow's first summer on Birch Lake doesn't start out well. Minnow wonders why her mother has sent her to spend her vacation with her grandmother and her great aunt and uncle. Especially when her mother has never returned to the cabin since leaving it as a young woman. But the summer turns beautiful as Minnow comes to realize that the cabin is her home in the truest sense, and that the “geriatrics,” her elderly relatives, are her closest friends. Minnow discovers three goals for the summer: to swim across the lake to Picnic Island, as her mother did every summer when she was a girl; to get Anna, who has been mute for decades, to speak; and, finally, to bring together her long estranged mother and grandmother.