Afire alert disrupts the Venice screening of One to One: John & Yoko, Kevin Macdonald and Sam Rice-Edwards’ documentary about Lennon’s rambunctious post-Beatles heyday, when he and his artist wife Ono were first putting down roots in New York. Inside the hushed screening room, the flashing red lights and blaring alarm provide the second big surprise of the night. The first was how much I was enjoying the show. Short of a documentary that unearths incontrovertible new evidence that he faked his own death, I’m not convinced that the world needs another John Lennon film. The medium, surely, has him well covered already. But Macdonald and Rice-Edwards have managed to find and mine a rich source of material, tightly tucked away amid all the other wildcat wells. Their film turns back the clock to the early 1970s and a benefit gig that occurred around the time of Lennon’s deportation battle with Nixon (see previous documentaries for details) and his extended lost weekend with May Pang (ditto). Crucially, too, it throws this concert against the maelstrom of the US political scene, with a channel-surfing aesthetic that skips from car and Coke commercials to the Attica prison riot and the near-fatal shooting of Alabama governor George Wallace. While Lennon claims that he spent his first year in New York mostly watching TV, One to One suggests otherwise. Instead he hit the ground running, hurling himself at the action to become the standard bearer and figurehead for whatever progressive leftist cause was doing the rounds that week. The film blends archive footage with a trove of previously unheard phone conversations to show the ways in which he and Ono leveraged their celebrity status and surrounded themselves with a crew of colourful upstarts, from Allen Ginsberg to Jerry Rubin. The oddest of these, perhaps, is the activist AJ Weberman, who is tasked with a mission to raid Bob Dylan’s bins in order to prove what a “multimillionaire hypocrite” the singer has become. Ono pleads with Weberman to apologise, explaining that they need Dylan to perform at a planned “Free the People” concert in Miami, but AJ is unrepentant and initially won’t be budged. In the event, the Free the People event was cancelled. But Lennon promptly finds a new focus with the One to One benefit for disabled children from the Willowbrook state school. Macdonald and Rice-Edwards have remastered Phil Spector’s muddy original recording so that the footage now plays with a fresh, bullish swagger. This was Lennon’s first full-length concert since the Beatles performed at Candlestick Park and, it transpired, the last he would ever play. If only more nostalgic music documentaries could muster such a fun, fierce and full-blooded take on old, familiar material. One to One, against the odds, makes Lennon feel somehow vital again. It catches him like a butterfly at arguably his most interesting period, when he felt liberated and unfettered and was living “like a student” in a two-room loft in Greenwich Village. He’s radioactive with charisma, tilting at windmills and kicking out sparks. That’s maybe what triggered the fire alert. The ushers became nervous and felt they had to turn on the sprinklers.