Documentary filmmakers are, by definition, an adaptable people. Rolling with the unscripted punches of real life kind of goes with the territory – they just have to make sure they have a camera on hand to capture them. But even the most seasoned and perspicacious of documentarians occasionally get caught off guard, and such was the case for Oscar-winning director Alex Gibney while working on the Lance Armstrong project that became – after a series of quite unexpected developments – “The Armstrong Lie.”

Of course, that wasn’t the title all along. In 2008, months after he won the Academy Award for his harrowing torture study “Taxi to the Dark Side,” Gibney began work on “The Road Back,” a film intended to be a mostly admiring portrait of the seven-time Tour de France champion as he prepared for a comeback from retirement and an eighth victory in cycling’s greatest race. Needless to say, things didn’t quite pan out that way. Armstrong finished the 2009 Tour a respectable but personally disappointing third, but that was the least of his troubles, as the doping allegations that he had strenuously denied throughout his career became ever more compelling and, in time, impossible to dismiss.

That left Gibney, to all intents and purposes, high and dry: the New Yorker had a heap of raw material for a celebratory film about a figure whom, it appeared, was hardly worthy of celebration. Gibney shelved the project, but didn’t abandon it. As the Armstrong case grew more complicated, and its consequences more severe, the director saw he had the makings of a rather more unusual film about the fallen idol – one that could use its own interrupted development to reveal how Armstrong pulled the wool over the world’s eyes, Gibney’s included. As such, it requires the filmmaker to play both puppeteer and patsy, breaking form by foregrounding his own relationship to his subject – “The Armstrong Lie” may be as deliberate and insightful a work as we’ve come to expect from Gibney, but it’s colored by his sense of personal disappointment and professional pique.

The irony, explains Gibney, is that this unforeseen turn of events wound up making for a film that was, in a sense, more typical for a filmmaker accustomed to taking a tough line on tough subjects. “A feel-good story would have been unusual for me, and I was actually looking forward to that,” he laughs over the phone from New York. “So in a funny way, when the shift came about, it came back to more familiar territory for me.”

Still, he’s quick to point out that even at the beginning of the process, he never had “a Disney film” in mind. “Even in the first film, I dealt with the allegations of doping,” he says. “The title ‘The Road Back’ had a double meaning, referring to both the comeback and the road back into the past. I liked the idea of a redemption story: the idea of a guy coming back at an ‘advanced age,’ and doing it clean, as if to prove that he was great no matter what. That was an interesting quest to observe, as long as I could deal with the allegations – which I thought he was confronting. I thought that was one of the reasons for his comeback: that, from his point of view, it didn’t matter if he’d doped in the past.”

While that essential thesis for the first film turned out to be entirely false, that didn’t mean Gibney couldn’t use it. “It wouldn’t have done any good to start from scratch,” he explains. “I had to make room for the film I’d already done – that’s part of the unique contribution I could make to the story of Armstrong. I had all this wonderful footage that no one else had, that cast a completely different light on his story. I just had to integrate that into a more familiar investigation.”

Guy Lodge is a South African-born critic and sometime screenwriter. In addition to his work at In Contention, he is a freelance contributor to Variety, Time Out, Empire and The Guardian. He lives well beyond his means in London.