“A wonderful life, wonderfully told” would be high praise for any biography, and richly deserved for Evan Thomas’s “First: Sandra Day O’Connor.”

So good is the work that, as I read, I grew to admire O’Connor more even as my qualms about her jurisprudence increased. Thomas had found what Leon Edel called “the figure under the carpet.”

Having taught constitutional law for almost a quarter-century, I am very familiar with the Supreme Court justice’s role in many 5-to-4 decisions and the opinions she wrote. The general outlines of the court’s divisions have been understood and well-reported for a couple of decades in many fine books. But “First” is now first among equals. In fact, my future con law classes will begin not with Marbury v. Madison, as is common in the nation’s law schools, but with “First,” for in it they will find what I try all semester, every year, to convey: The Supreme Court is a collection of nine very human beings trying their best to buttress the “rule of law” as they understand it.

Of course, they don’t all understand it the same way, or we’d have nothing but 9-to-0 decisions, and while those displays of unanimity do occur, they are uncommon. How do nine people of good intent divide so often and so deeply? Thomas explains this, and in a way that a layman can not merely understand but genuinely enjoy. I sped through “First,” but my wife, not a lawyer, beat me to the end. That’s because, as Thomas told me on air, “It’s a great love story,” and we both love those.

Actually, it’s many love stories that instantly draw you in: O’Connor’s love of her parents, of the vast Lazy B ranch where she grew up, of Stanford, her three boys, her large circle of dear friends — and especially her husband, John O’Connor.

For those of us who are absorbed by the court’s doings and study its decisions, the most impressive aspect of the book is its sources. O’Connor wasn’t the only one who sat down with the author — so did her sons, many of her friends, her legislator buddies from her days in the Arizona Senate and 94 of O’Connor’s 108 Supreme Court clerks.

Even more astonishing, O’Connor threw open her court files to Thomas — an unheard-of level of access to all the bench memos, draft opinions and file memos from the day she took her seat in 1981 until the arrival of the longest-serving justice now on the court, Clarence Thomas. This discreet courtesy to still-serving judges, we learn, is quintessentially an O’Connor touch.

Thomas also had O’Connor’s journal of life on the court, which she stopped keeping after a few years. But more important by far, Thomas was given all of her husband’s detailed diaries.

In John O’Connor’s journals is a second biography, every bit as crucial as his wife’s. Their love and respect for each other blazes in the pages. So does their humor. So does the difficulty of deciding the toughest cases in this era of the Supreme Court — the abortion and affirmative action cases. John saw and heard all of it, and he wrote much of it down.

Until he couldn’t, until Alzheimer’s disease got him fully in its grip. This is why everyone — not just those fascinated by the justice system — should read this book. I don’t think I’ve ever seen a story of a superb mind’s slow deterioration so touchingly conveyed, so achingly told. That the same disease has now begun to take the justice herself is doubly awful. But the book performs a great service: It illuminates the reality of a disease that is devastating an ever-larger number of Americans, and it provides an example of how a truly admirable couple handled a heartbreaking crisis.

But the book is not maudlin. Not in the least. It’s a chronicle of Bohemian Grove gatherings, golf, skiing, hiking — indeed, of endless activity; a tale of brilliant intellects in young brains, of gossipy clerk networks and of the essence of judging — rightly and wrongly. It’s a magnificent work of biography and political science, but also a story of suffering with dignity, of compassionate friends, devoted children, and the most dedicated of spouses. There is not a whiff of cruelty in these lives, though there is much disapproval of people who did not work hard or who turned the attention on themselves too much.

Come for the Supreme Court drama, revel in the wonderful portraits of all the justices with whom O’Connor served, but stay for the story of a life well and fully lived. Sandra Day O’Connor is a great American. So was John O’Connor. And Evan Thomas is a great biographer.

Read more:

Julie Cohen: The female Supreme Court justice who led the way for others

Charles Lane: A poignant exit for one of the most powerful women in the history of U.S. government

Ann Norwich: We’re not prepared for the coming dementia crisis