It’s impossible to watch this absorbing documentary about anti-Putin dissident Alexei Navalny without a terrible suspicion entering your mind: did Putin order his grotesque Ukraine invasion because of Navalny? Was it a diversionary tactic against the huge, growing wave of protest spearheaded by Navalny who, in 2021, had defiantly returned to Russia from German exile and whose instant arrest and imprisonment merely fanned the flames of his international celebrity? Putin was no doubt deeply enraged by this social-media megastar who had not only survived a Novichok assassination attempt but then humiliated the Kremlin by unmasking his malign and cack-handed would-be killers online.

Navalny is an extraordinary figure in many ways: approachable, telegenic and easygoing. Or mostly easygoing, anyway: he can still sound irritable and defensive when questioned about his appearances on the same stage as extreme Russian nationalists about 10 years earlier, and perhaps this film could have looked harder at the facts of Navalny’s early life. But the real eye-opener is the interview with the Bulgarian investigative journalist Christo Grosev of the website Bellingcat who managed such breathtaking feats of detection on Navalny’s behalf in finding the FSB assailants. Grosev is all about data: by getting hold of passenger manifests, travel details or call records – and everything digital leaves a trace – he can put together an objective picture, even retrieving the culprits’ passport photos.

It is quite staggering. And Navalny’s story has a particular resonance in Britain: he survived, but Dawn Sturgess did not – the blameless British national was fatally poisoned with Novichok on British soil in 2018, as the chaotic byproduct of a bungling attempt by Russian agents to kill former agent Sergei Skripal and his daughter Yulia in Salisbury. For so many reasons, Navalny’s story concerns us all.

• Navalny is released on 12 April in cinemas.