In “Without Precedent: The Inside Story of the 9/11 Commission,” the basic decency of the co-authors — a Republican and a Democrat who led the nation’s comprehensive, independent inquiry into the origins and roots of, and remedies to the attacks of September 11, 2001 — permeates the book.

The often gripping narrative provided by Thomas Kean, a Republican and former governor of New Jersey, and Lee Hamilton, a Democrat and former chairman of congressional panels on foreign affairs and intelligence, shows how tough it was for the nine-man, one woman panel to fulfill its ambitious, grim mandate and tell the heartbreaking saga of the attacks of September 11, in a “detailed, nonjudgmental way.” It also shows what can be accomplished when judicious people suppress their personal preferences and ideological differences for a greater good — in this case, trying to explain how and why the attack occurred and, one hopes, prevent ever more lethal assaults by Al Qaeda and other like-minded militant Islamists.

The book will interest not just those obsessed by September 11, but anyone seeking to understand how policy is made in Washington. A compelling account of individuals trying to balance competing pressures and temptations, it is also a primer for those committed to reform in these partisan, polarized times. But the co-chairmen’s calm and determined efforts to forge the unanimous consensus that ultimately resulted in the most sweeping reorganization of the nation’s intelligence bureaucracy in American history — whether the reforms are wise is another matter — came at a price, as even the authors acknowledge.

To avoid inflaming partisan furies, Messrs. Kean and Hamilton decided against confronting the White House and others who repeatedly stonewalled their requests for information. Rather than issuing subpoenas that would inevitably have prompted prolonged, fierce, and possibly losing legal battles, they chose painstaking negotiations. They also decided not to assign individual blame for September 11, but rather, to let the facts — and as was so often the case, differing interpretations of the facts — speak for themselves. While this approach ultimately enabled the panel to produce a consensus, and hence some of the bold changes adopted by a skeptical Congress and signed by an equally reluctant President, it often infuriated the influential families of victims of September 11 and others who cried out for accountability, if not revenge.

The authors’ “just the facts” approach also leaves some intriguing questions about the attack and the response to it unanswered. Among these is whether Vice President Cheney really issued an order to shoot down the hijacked planes after supposedly receiving authority from President Bush by telephone to do so, and if he did, why that order apparently was not transmitted to the nation’s military command until it was too late. Another controversy destined to linger is whether “Able Danger,” a once secret Pentagon program, identified one of the hijackers, Mohammed Atta, years before he entered the United States.

Throughout the book, Messrs. Kean and Hamilton write with a steady, sober voice, tracing the commission’s inauspicious beginnings — the original co-chairmen, Henry Kissinger and George Mitchell, both resigned after conflict-of-interest questions arose — to their fateful decisions to avoid partisanship by insisting, among other things, on a unified, nonpartisan staff. And what a staff it was. The authors credit their success partly to the dedicated group of 80 lawyers, analysts, and experts who sifted through 2 million pages of documents, conducted more than 1,200 interviews, devoured 900 “memoranda for the record,” dissected hours of classified tapes and transcripts, prepared more than a dozen politically charged public hearings, (one hour of a public hearing required 50 staff hours of preparation), and stayed in touch with concerned legislators, executive branch officials, families of victims, and others who closely followed the commission’s proceedings.

Readers meet, for instance, Navy Lieutenant Kevin Shaeffer, the only survivor in his section of the Pentagon that fateful day. After pulling himself out of the rubble with burns over 40% of his body, Lieutenant Shaeffer suffered two heart attacks and endured dozens of agonizing skin grafts. He had to relearn basic skills, such as how to button his shirt.Yet he volunteered to work on the commission, where he wound up reviewing the emergency response to the catastrophic strikes in New York and on the Pentagon. “He ended all his emails with ‘Never Forget,'” the authors write.

The staff and the commission, in turn, benefited from having leaders who supported them against unfair, often politically inspired attacks. Because of the co-chairmen’s staunch support, Democratic critics and some of the families of victims failed to oust the panel’s talented executive director, Philip Zelikow, a historian who had worked at the State Department and at the White House with Condoleezza Rice and other Republicans. A similar, but particularly ham-handed effort by the attorney general, John Ashcroft, to unseat Jamie Gorelick, a senior Justice Department official under President Clinton and the September 11 panel’s only female commissioner, also failed.

While the book contains little new information about September 11, Messrs. Kean and Hamilton disclose that they split on only one issue: whether to issue a subpoena for documents to the North American Aerospace Defense Command, the Pentagon agency partly responsible for protecting America’s skies, which, along with the FAA, resisted turning over documents for months and whose commanders gave the panel inaccurate testimony they were subsequently forced to retract. The panel voted 6–4 to issue the subpoena, with, paradoxically, Mr. Kean, a Republican, voting for the subpoena and Mr. Hamilton, a Democrat, voting against it.

Another struggle occurred over access to the now notorious “presidential daily briefings,” the daily summaries of threats and key events the CIA gives the president and other senior officials six mornings a week. The ever-protective Bush White House refused the panel access not only to its own PDBs, and also those of Mr. Clinton. An elaborate compromise that gave only a few members of the panel access to the documents, which otherwise remain confidential, was eventually struck. A similar compromise also was negotiated over a meeting with Mr. Bush — the “client,” as the then-White House counsel and now attorney general, Alberto Gonzales, called him — and with Mr. Cheney, both of whom initially resisted appearing before the entire panel and wanted to limit any session to one hour. The meeting lasted longer in the end, and the White House ultimately agreed to meet with the entire panel. But neither Mr. Bush nor Mr. Cheney were under oath, and they insisted on testifying together. The book, alas, sheds little light on what they told the panel.

Stonewalling, of course, was not unique to the White House. The book documents the panel’s struggle, among others, over timely access to documents collected by previous congressional inquiries into the attacks of September 11.The authors also bemoan “over-classification,” which they complain promotes wild conspiracy theories. Occasionally the authors’ fury, which they understatedly call their “frustration,” with such bureaucratic antics is obvious.

Again and again, the book highlights the key role played by the families of victims, without whom the commission would probably not have been created or been successful. A source of evident frustration at times, the families repeatedly provided the pressure needed to wrest documents from a recalcitrant agency, to force the White House to comply with some of the panel’s demands, and, ultimately, win congressional approval of the reorganization of the intelligence community, which several earlier commissions had urged to no avail. But as the book indicates, the panel’s relationship with these families was often tense.

Messrs. Kean and Hamilton write that the threat posed by militant Islamists — perhaps armed with the weapons of mass destruction Al Qaeda was actively seeking — continues to grow. So, too, does the authors’ mission: to continue lobbying for the changes the panel urged and other steps to enhance America’s defenses.

On several key points of disagreement with the White House, the chairmen remain adamant: While their staff members uncovered “disturbing evidence about connections” between Al Qaeda and Iran, as well as contacts between Al Qaeda and Iraq before September 11, they found, contrary to the administration’s repeated claims before and after the 2003 invasion of Iraq,”no collaborative, operational relationship between al Qaeda and Iraq.” The chairmen stuck to their view even after Mr. Cheney suggested that he might have information the panel lacked, a claim the chairmen clearly reject and which Mr. Cheney has not repeated.

Messrs. Kean and Hamilton are quick to add that they were in no position to assess the decision to go to war in Iraq. “We were the 9/11 Commission, not the Iraq War Commission.” They clearly had enough with September 11; but perhaps given their contribution to our understanding of the attacks and the impact on how intelligence is now gathered and analyzed in the wake of September 11, they should be called back into service for another independent, dispassionate inquiry into the venture that now so roils and divides the nation.