A LAWYER’S MIND: Robertson is the first biographer of the man who anticipated our Founding Fathers.

Geoffrey Robertson, a British human-rights attorney, has drawn from an array of primary sources for his reinterpretation of the life of a man not quite lost to history. Much can be made of its relevance to current events, in which we seek to prosecute malevolent presidents and dictators under the law rather than assassinate them in their beds. We owe this dignity — and many of the protections in the US Constitution, as well as the right to an attorney, and even public registries of land ownership — to Cooke.

He has till now been remembered by a single word: “regicide.” He did, after all, invent a new crime, tyranny, and then accuse Charles I of having committed it. The king’s refusal to recognize the court and the court’s failure to assume innocence rather than guilt (which would have been another innovation) condemned Charles to the ax in 1649.

Robertson is the first biographer of Cooke, whose legal-reform efforts predate and rival those of the American Founding Fathers. (Some are so far-reaching that they remain unfulfilled, such as having lawyers spend 10 percent of their time helping the indigent.) For the better understanding of the real roots of American democracy alone — and where we have gone astray since — this book is more than worth the read.

But Robertson goes farther, delving into tiny, gruesome details and bringing a lawyer’s mind to the task of reviewing their significance. Although many historians have marveled at the efforts to which the Parliamentarians went to create a legalistic air about the trial of Charles I, none has so minutely described the machinations by which the Puritans massaged the law, the Bible, and their own consciences in the effort to do right, in the right way. Robertson sheds new light on how devotion to the law and to the word of God gave the Puritans’ life daily meaning, and he chides historians for not discovering what he did.

Although religion was the starting point of 17th-century religious reformers in England, morality became their watchword, and ruthless logic their method. But the English Puritans (a separate group from the Brownists, a tiny sect who later became what we know as the Pilgrims) got in their own way while trying to improve the godliness of their government. In the middle of the Civil War, some Puritan thinkers realized that what they really wanted was to restore the king to the throne. But they also realized that he would never accept the constitutional-monarchy constraints Parliament was seeking to impose.

What to do? Finding someone to sneak in and stab the king or poison his food was not acceptable. Instead, they found a lawyer to put the king on trial. That lawyer was Cooke, whose sense of logic and justice was so powerful that even when on the scaffold himself in 1660, about to be hanged, drawn, and quartered at the hands of the Restoration, he comforted other condemned men and encouraged his family to rejoice that he was going to meet his beloved God.

The Tyrannicide Brief: The Story of the Man who Sent Charles I to the Scaffold | By Geoffrey Robertson | Pantheon Books | 448 pages | $30