When the oncologist David Agus first met Elizabeth Holmes, in the green room of a health conference, he found a pleasant, easy woman who seemed to belong to an ordinary afternoon. Minutes later, on stage, she had become somebody else: the accent shifted, the voice dropped into a grave, husky register, and the warmth gave way to a kind of rehearsed gravity. "It was as if I had met a person and then interviewed a separate person," he recalls, and he had never witnessed such a transition before. That doubleness sits at the heart of the Theranos story, and of You Can See Everything, a strange new documentary released in the United States this week.

It was directed by the absurdist comedian Nathan Fielder together with Lance Oppenheim, and it was filmed during the 34 days before Holmes was due to report to a federal prison camp in Texas to begin an 11-year sentence for wire fraud and conspiracy. The outcome would have seemed unthinkable in 2003, when a 19-year-old left Stanford University to found a company promising hundreds of blood tests from a few drops, and went on to charm investors and board members from Rupert Murdoch to Henry Kissinger. Part of the spell, the historian Margaret O'Mara suggests, lay in timing. Silicon Valley was then dominated by men and hungry for innovations more consequential than social networks, and Holmes arrived dressed in the black turtleneck of Steve Jobs, offering to heal medicine itself.

Her investors saw a visionary; the technology, it turned out, saw very little. Yet the scandal has always been as much about audiences as about its heroine. If a persona can be built so skilfully that billionaires, statesmen and doctors cannot see through it, how much of what we call charisma is simply our own wish to believe?