This book earned starred reviews at School Library Journal, Kirkus and Publishers Weekly, and I can tell you why: it rocks, plain and simple. Hmm, where to start.
I think I'll begin with the subtitle, and tell you that this book is based in large part on the observations of Susy Clemens, the daughter of Samuel (a.k.a. Mark Twain), who wrote her own biography of her father when she was 13 years old. Barbara Kerley found that information and followed it to its natural conclusion: a book about Susy writing the biography of her father. It's the perfect sort of biography, really, because it is a biography of a biographer and her subject all at the same time: a child's-eye view of Twain from a person who knew him best. And when Susy's father cottoned on to what she was up to, he made comments just to help her along with her biography. About Susy as a biographer, Clemens said: "This is a frank biographer and and honest one; she uses no sandpaper on me."
I'm going to skip next to one of the things reviewers don't often talk about explicitly (unless it's a pop-up book), and that's book design. Moreover, I'm going to start with dimensions, so that you'll understand what the weird little device is in this book that works so very well. The pages measure 8-1/2 x 12, which means that the book cover is slightly larger in each dimension. But every few pages, there's a two-page insert that measures only 4-1/2 x 5-1/2, which is an excerpt from Susy's Journal. The "cover" says "Journal", the inside two-page spread is an excerpt from Susy's actual journal using LinotypeZapfino One, a sort of semi-script printing that preserves Susy's exact words and spellings (even when they're a bit "off"). There are eleven journal inserts in all, which add so much information and character and charm to this book. Here's the text from the last one in the book:
The other day mamma went into the library and found papa sitting there reading a book, and roaring with laughter over it; she asked him what he was reading, he answered that he hadn't stopped to look at the title of the book . . . she glanced over his shoulder at the cover, and found it was one of his own books.Susy told it like she saw it, and it adds so much dimension to the real Samuel Clemens - as does the way Kerley weaves additional quotes into the main text, relating details in a cogent, coherent way - that the book is a delight.
Further contributing to the delight are the marvelous illustrations by Edwin Fotheringham, whose work on last year's Mermaid Queen, by Shana Corey, I raved about. Here's the first two-page spread from the text, which establishes the set-up of the book and what inspired Susy to write her father's biography in the first place.
Kersey notes that Susy documented both Twain's public life and Clemens's private life. She talked about his early years ("Papa was born in Misouri . . . And we know papa played "Hookey" all the time and how readily would papa have pretended to be dying so as not to have to go to school!"), his speaking engagements, his books - and her opinions on them ("She loved The Prince and the Pauper for its 'lovely, charming ideas' and beautiful language.") - and she wrote of their home life, and what Clemens was like in private. That included, of course, his writing habits:
I adore almost everything about this book: The text, the design, and the illustrations I've already discussed. But the book includes a phenomenal Author's Note at the end, which provides information on Twain and on Susy Clemens, who died of spinal meningitis at the age of 24. As the Author's Note says (grab a tissue - you've been warned):
For the rest of Twain's life, he treasured the biography, misspellings and all . . . The loss of Susy  may have been the hardest for Twain to bear. After her death, he wrote to a friend, "I did not know that she could go away and take our lives with her, yet leave our dull bodies behind. . . . My fortune is gone, I am a pauper."Kerley also provides a guide to "Writing an Extraordinary Biography", which offers tips to children who wish to write a biography. It's not only available in the book, but also on Kerley's website. The final page in the book (which would ordinarily have been an endpaper, but they used every inch of this book, so there's actual content printed inside the back cover!) contains "A Selected Time Line of Mark Twain's Life" and a family photograph (along with dedications, copyright info, etc.), and the inside of the back cover provides a bibliography of sorts - a list of "Sources" for every single quote contained in the book, including the author's note.
My one quibble with this book (and longtime readers won't be shocked to hear it) is that the book lacks page numbers - something that's particularly troubling when the "Source" list at the back of the book references the pages by number. It wouldn't have been hard to add them to the book, and it would help to sort that out more quickly. *shakes fist at editors and book designers over this picayune point*
You can see a few more spreads from inside this book at Edwin Fotheringham's website (select "Children's Books" from the left-side menu, then scroll through. You can embiggen any of the images by clicking on them after you select them.) And here's a link to the New York Times review of this book, if'n you're interested.