Any film "based on a true story" is going to take some serious liberties in telling the story of someone who existed. Some decisions are understandable given the limited running time of a film and the need to compress certain elements. Other decisions can move a story so far away from real life that it barely resembles what really happened. Red Joan aims to tell the story of Melita Norwood, known as the "granny spy" but comes up short pulling more from Jennie Rooney's novel of the same name and less from history.
This is a shame since the real story is pretty interesting and Red Joan is rather dull. Trevor Nunn casts Judi Dench in the title role but strangely squanders any of her talents by only using her in the framing story and keeping her reserved. Sophie Cookson is the real lead as the younger Joan.
As the film opens, Dench is tending to her garden when her life changes for the worse when the police show up and drag her off. While she may look like a granny, she is not an innocent one. As Dench is interviewed, the film flashes back to Joan's college years. Joan is a smart physics student who gets pulled into a Communist group via Leo (Tom Hughes). Leo changes Joan's entire existence with his big ideas.
The intercutting back to the interrogation is one of the film's biggest problems. Dench is dull here, often forced to just react to the memories we see played out. Cookson does a better job in making Joan a compelling figure but Lindsay Shapero's screenplay never crackles with suspense or tension. This is a surprise given the intrigue built into this story. The film does explore a bit of how Joan was able to go undetected for so many years due to being a woman but that strand never culminates into anything significant. Instead, Nunn's film chooses to forego any suspense in favor of giving Joan a chance to atone. This moment is clunky, even including a crowd shouting the film's title at her.
Red Joan is a missed opportunity. How the film makes Dench so dull is the only remarkable thing about it. The shame here is that this story really is interesting and some of the stuff with younger Joan works.