‘Man on Wire” is an upside-down documentary, so riveting in its setup and exposition that the climax arrives almost as an afterthought. The man of the title — the famed French tightrope walker Philippe Petit — is ultimately less interesting than the drama surrounding his wire, a tightrope strung between the newly completed World Trade Center towers in August 1974. And rather than tease the audience through to a rousing finale, the director, James Marsh (“Wisconsin Death Trip”), seems to embrace the pure drama of the concept — the methodical, grueling, and illegal preparations that went into making Mr. Petit’s artistic daydream a reality.

Much like the documentary “The Gates,” which made its premiere at last year’s Tribeca Film Festival and captured not only the magic of an orange-clad Central Park but the daunting year-by-year fight that pitted artists Christo and Jeanne-Claude against their critics in a very public political brawl, “Man on Wire” matches the spectacle with the behind-the-scenes struggle. Just as New York City was initially hesitant to put up all those orange panels, so was the security at the World Trade Center unlikely to grant Mr. Petit approval to ascend the structures and walk between them without a safety net. So he tackled that problem in inspired fashion: He didn’t bother asking for permission.

Mr. Petit is an eccentric personality, and the movie is as much about his telling of this “true story” as it is about the reality of the moment. Recounting the feat in first-person detail, he embellishes and augments the facts as any great storyteller would, and we see the way his wide-eyed idealism about ascending these new towers (the first tenants moved in during late 1970) quickly transitioned into pragmatic cynicism. Standing proud at 110 stories, presiding over New York as the nation’s tallest buildings, the WTC was surrounded by intense security, and Mr. Petit knew that gaining access to the roof would be no easy task. So he and his colleagues shifted gears, imagining the mission as if it were a bank heist.

Needing entry to both buildings, and a way to haul a considerable load of equipment to each roof, Mr. Petit and his co-conspirators started casing the buildings. They surveyed the security of the lobbies, researched the required credentials to gain access to the elevator banks, and then went about renting a van and opting for a plan that would breach the WTC defenses from underneath, in the parking garage. On the night of the break-in, they came within a few inches of being discovered by security guards on one of the building’s top floors, which was still under construction, and had to deal with unexpected gusts of wind that grew more violent as the evening wore on.

All the components of a riveting heist film are here. There’s a well-laid plan that runs afoul, conflicts among the criminals that blow up mid-heist, and unexpected complications that heighten the drama. The fact that it’s all true only makes it more exciting — so exciting, in fact, that we almost forget the simple majesty of what Mr. Petit set out do in the first place. As Mr. Marsh weaves together black-and-white re-enactments with first-person recollections, still photos, and archival footage of Mr. Petit’s reconnaissance missions to the World Trade Center, the nitty-gritty of the break-in interacts playfully and effectively with the poetry of the mission. It’s no surprise that “Man on Wire” took home both major documentary prizes at this year’s Sundance Film Festival — the award from the jury for its skillful craft, and the award from the audience for its sheer thrills.

“Man on Wire” is a marvel of pacing and personality, and also an emotional celebration of a structure we have spent the past seven years mourning. Yes, it’s a thrilling story of a crime being planned, executed, and altered at the last second. It’s an absorbing story of art and imagination, about an artist committed to a dream and willing to risk everything in a bid to realize it. But it’s also about the source of Mr. Petit’s obsessions, a film that makes it okay for us once again to think about the towers not just as places of death and devastation, but as sources of wonder and astonishment.

The more rapid his narration becomes, the more we see the degree to which Mr. Petit loves his fame, his smile growing wider as the film’s plot grows thicker. But with the commitment and perseverance on display here, it’s also obvious that the World Trade Center walk was more than just a job for him. Unfolding so high in the sky that many onlookers couldn’t make out his shape 110 stories up, Mr. Petit’s plan went well beyond attracting an audience. There’s a bittersweet denouement to the tale that suggests this was the unparalleled high point of his career — and perhaps even his life. As his momentary dance in the clouds comes to a conclusion, things start to fall apart around him, and it will be hard for audiences not to experience a similar letdown.

In “Man on Wire,” the towers are more than just steel and glass. They mean something spiritual to Mr. Petit — and so they did to the city in which they stood. During his euphoric, 45-minute stroll between them, we fondly recall all they stood for. As he comes down in handcuffs, we reckon once again with what’s been lost.

ssnyder@nysun.com