In the fall of 2020, when the Canadian filmmaker Daniel Roher was in Europe doing research for a film project that never materialized, he met Christo Grozev, a Bulgarian investigative journalist.
Mr. Grozev asked Mr. Roher if he knew who Alexei Navalny was, referring to the Russian opposition leader who had been poisoned, almost fatally, while in Siberia. When Mr. Roher answered affirmatively, Mr. Grozev said he thought he knew who might have poisoned Mr. Navalny, who was, by then, slowly recovering in relative seclusion in Germany's Black Forest.
Recalling that meeting between Mr. Roher and Mr. Grozev, Diane Becker, one of the producers of the documentary "Navalny," said, "Daniel asked, 'Who's making that movie?' Christo said, 'Let's find out.' They were soon driving across Europe to meet with Alexei, his team, and his family. The rest is history."
That spellbinding history, captured in real time by the filmmakers and Mr. Navalny's team, is the core of "Navalny," which will be shown Saturday evening as part of HamptonsFilm's SummerDocs series.
There was no time for the filmmakers to do preliminary research for the story. "It was really just one of those situations where you're in the right place and you have to keep the cameras on and be there and see what unfolds," said Ms. Becker.
Mr. Roher and Odessa Rae, another of the film's producers, were embedded with Mr. Navalny and his team, which included Mr. Grozev and Maria Pevchikh, the head of Mr. Navalny's Anti-Corruption Foundation, from October 2020 until mid-January 2021, when Mr. Navalny returned to Moscow, where he was immediately arrested and subsequently imprisoned.
He'd been on a flight from Siberia to Moscow in August 2020 when he became violently ill. Cellphone footage captures his agonizing screams and the chaos on the flight, which made an emergency landing in Omsk, where he was hospitalized in a coma.
He was eventually transferred to a hospital in Berlin, and from there, once sufficiently recovered, he and his family settled in the Black Forest. With a combination of newsreel film and footage shot by his team, the filmmakers were able to fill in his back story, including scenes of rallies where he whips up his supporters with denunciations of the people in power as "corrupt thieves."
"Maria and Alexei and his whole team are really media savvy, they make a lot of YouTube videos reporting on things they're working on. So when the whole thing went down, Maria was filming everything on her phone." Ms. Becker said.
What went down was spurred by Mr. Grozev's determination to identify the poisoners. It's a complex, suspenseful, but fascinating investigative process that eventually uncovers evidence of several members of Russia's Federal Security Service having traveled to Siberia at the same time as Mr. Navalny.
"We had no idea beforehand whether we would find the evidence we were hoping to find," said Ms. Becker. After several fruitless phone calls to security agents, Mr. Navalny tried a "Hail Mary," pretending to be an official in Russia's National Security Council and calling a scientist whose name had surfaced as a possible participant in the plot.
Before that call, according to Ms. Becker, "Christo said, 'This could be a fool's errand, because these guys don't talk.' " Remarkably, and to the astonishment and glee of Mr. Navalny and his team, the scientist did talk -- for 45 minutes, during which he named others involved in the poisoning and said he was sent to clean things up.
Once the evidence was in hand, all of it recorded, "We knew this story was important, and we knew we needed to get it out as quickly as possible. We had a small team of trusted people we had worked with before, because we knew we weren't going to be able to talk about this project at all."
Mr. Navalny's team released the evidence to the media in December 2020.
"Navalny" premiered in January at Sundance, where it won the documentary audience award and the festival favorite award. It was released on CNN in North America in April.
The SummerDocs screening will take place at Regal UA East Hampton cinema on Saturday at 7 p.m. to be followed by a conversation with Mr. Roher, David Nugent, HamptonsFilm's artistic director, and Alec Baldwin. Tickets are $35.
