Twin towers of blue light penetrate the night sky, slightly to the right of the place they memorialize. If I walked to the front window of my city loft I could see them angling up as I used to see the north tower, night and day. I can’t make myself do it. I don’t know why, exactly.

Shortly after the disaster, when we caught our breath and there was talk of a fitting memorial, I told my family I thought there should be holograms of the towers shining into the night sky. I liked the idea of the impenetrability of light. I still like the idea, but the reality is too painful, a ghostly reminder of what happened.

We watched the documentary “9/11” last week that commemorated the sixth month since 9/11. I was ambivalent about watching, afraid of stirring up the effects of the trauma while curious about those last moments inside the buildings. This documentary was much more than an account of disaster; it had the dramatic structure that real life rarely provides.

The filmmakers, brothers, started out to make a documentary about a rookie firefighter. After many interviews they found their man in Tony, a sweet, big, hopeful romantic, who wanted to be a hero. Their film follows Tony as he joins Ladder 1 on Duane Street in lower Manhattan and documents his days on the job.

We watch as he is gently hazed by his colleagues and made to do the grunt work at the station house. We watch as he waits. He waits for his first fire. Firefighters talk of two kinds of “probies” (as they call the probationary firefighters); the white clouds and the dark clouds. One kind brings fire, the other none. Tony is turning out to be a white cloud. Over the summer of `01 there are no fires of any consequence on Tony’s watch. The filmmakers are running out of material.

The suspense built by waiting is doubled by the firehouse fable that says when there is no fire for a long time, a big one is coming, and by our knowledge of the future. Finally, on September 11, there is a gas leak call to Lispenard and Church Street. One of the filmmakers rides with Chief Pfeiffer to investigate. As they are filming, the sound of the jet can be heard and the camera tracks it as it flies into the tower. Ladder One is first on the site, leaving only Tony (and his shadow cameraman) to man the station.

His agony is palpable as he watches the scene unfold on TV, and he is unable to help. In a twist, a retired battalion chief shows up at the firehouse after the collapse of Tower Two, and in an act of foolish bravado takes Tony and the filmmaker with him to the site. Through the lens of the first filmmaker, we see the rest of the company survive the first collapse and escape minutes before the second. We are left in suspense as all the Ladder One crew comes back alive, all except Tony.

Day turns to dusk and each filmmaker fears the other’s loss before they are tearfully reunited as Tony walks down the block covered in white ash, alive and well. As it happened, the house lost no one that day, spared by being one of the first companies to respond, and therefore in the first tower to be hit, the second to go down.

Watching the film is cathartic as only theater can be, giving us a story of hope and renewal out of an experience of despair. That it is real life is a deeper mystery.