Meanwhile, firefighters, carrying impossible 90-pound loads, perished. The book’s most indelible image is that of a hundred fire fighters, exhausted, resting on the 19th floor of the North Tower. Because of obsolete walkie-talkies, they didn’t know about the South Tower’s collapse.

Here, verbatim, is the scene as court officers Baccellieri, Moscola, and Wender, who’ve come down from floor 51, reach floor 19, and see the resting firefighters:

Most were sitting, and had stripped off their turnout coats. Helmets off. Some were down to their blue T-shirts, maps of sweat blotting through the fabric emblazoned with the Fire Department shield. Wender saw that some were lying down. Axes resting against oxygen tanks. They could not be hearing, Wender thought, what we are hearing.

Baccellieri and Moscola took in the scene. They guessed there were at least 100 firefighters on the floor.

“We’re getting out of here,” Baccellieri yelled. “We’ve been told we’ve got to get out of the building.”

No one moved.

Baccellieri, Moscola, and Wender survived. All 100 firefighters died. Reason being no one told them that the tower they were in was already leaning and, near the top, buckling.

In spare, eloquent prose, the authors reconstruct these scenes. And unlike the moronic football fans who, in weeks following the attack, painted their faces red, white, blue — as if the post-9/11 trauma were a football pep rally — they never romanticize. They tell the truth: the firefighters, though brave, marched with way too much equipment to their doom. Office workers, like the poor souls who worked for Mizuho, descended to the lobby and were told to go back, where they died. Jumpers leapt to their horrific deaths, not because they were brave, but because the heat was unbearable. The towers, because of design flaws, were ripe for collapse. Most ordinary people, such as Abe Zelmanowitz, who, rather than saving himself, stuck by his quadriplegic friend Ed Beyea, acted with heroic unselfishness. Someone oughta build a statue to these guys.

And someone oughta give Dwyer and Flynn one of those fancy writing awards. They explain, in layman’s terms, the reasons why the buildings collapsed, the unique architecture, the lack of fire-proofing. And over everything they write hangs the first World Trade Center attack in 1993, the attack that should have spurred the fire-proofers to work doubly fast; they didn’t. By Sept 11, only 20 floors had been adequately fire-proofed. This appalling ineptness, along with corrupt building codes from the 60s—including bunching elevators and staircases at the buildings’ cores to increase rentable office space—killed thousands.