IT'S A LITTLE SLOW, the first half-hour of Man on Wire by James Marsh. Stick with it, though, because the slight complications in the setup are small compared to the glory of Philippe Petit's 45-minute walk along the edge of infinity between the Twin Towers in New York. It happened on Aug. 7, 1974: a stroll of 200 feet, with the fine chance of a fall 1,776 feet straight down. Petit planned this caper—"Coup" is the word he used—well. So well, despite it all, the setup has a slight routine quality. If the planning didn't go like clockwork, at least it went without major hitches. No one on Petit's team developed a sudden heart condition or turned out to be a police snitch, as in the heist movies the acrobat loved. The early part of the documentary shuttles between the planning stages and the long night before the event itself. It's amazing enough that Petit did this stunt. Maybe it's more amazing when you learn he didn't sleep the night before. Petit is a physically small man, now wizened, but still with a resemblance to the Malcolm McDowell who put up such a fight against authority in 1960s cinema. A Parisian street performer, Petit carried out his most unforgettable stunt after starter capers, like walking between the towers of Notre Dame de Paris and strolling in the air between the pylon and the crest of the Harbor Bridge in Sydney. Fortunately, Petit kept movies of both these events and of the planning stages of the New York event. His headquarters was a pasture in Auvergne. We see him driving a tractor past a dirt-road turnoff, marked by a cardboard placard: "World Trade Center Association." In this pasture, Petit and his team solved one problem that haunts the mind ever since first hearing about this stunt: How the hell did they get a cable across? (Answer: bow and arrow and monofilament attached to a rope attached to a cable.) Man on Wire—the title comes from the deliciously terse NYPD police report—begins to accelerate, finally, as Petit's lover, Annie Allix, describes her own fears. She was nervous about the quality of Petit's helpers: one was "fumé"—stoned on marijuana when she met him. And at the end, it's her eyewitness account of Petit's space walk that tears us up the most. Sometimes we lose the one we love through death. Sometimes, it's through near-death experiences.

For music, the film reuses soundtrack compositions by Michael Nyman from The Cook, the Thief, His Wife and Her Lover and Drowning by Numbers. Speaking of numbers, a real cornball one, Erik Satie's Gymnopedie no. 1, accompanies the walk itself. Petit's never-to-be-repeated feat refreshes a dreadfully overused musical composition, making it beautiful once more. From the moment after he was arrested, Petit noticed that Americans asked why he did it, instead of celebrating the artistry. Petit gets to keep his secret. Marsh, who did the excellent adaptation of Wisconsin Death Trip, never asks the other obvious question that so many of us would ask—those of us who get shuddering vertigo just thinking about the sound of the wind up there and the far-off noise of streets below.

MAN ON WIRE (PG-13; 90 min.), a documentary by James Marsh, opens Friday at Camera 7 in Campbell and the Aquarius in Palo Alto.

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