This drama is slow-burning enough to get mistaken for boring, but patient viewers will find an intriguing, unique dilemma at the center of this ripped-from-the-headlines spy story. It's easy enough to condemn Joan (and the woman who inspired her character, Melita Norwood) at face value -- she is, after all, a British citizen who gave her country's wartime enemy the intelligence it needed to make an atomic bomb. But the more we learn about Joan, the more sympathetic she becomes. Deeply committed to an idealistic strain of communism, her motive is only to level the worldwide playing field. If everyone knows how to make a bomb, she reasons, everyone will be too afraid of reprisal to actually detonate one.
Playing a woman whose fiery politics have cooled after many decades of living an unremarkable life, Dench, as always, is impossible to look away from. But her scenes mostly take place in gray interrogation rooms or around her suburban house. Cookson, meanwhile -- beautifully dressed in perfect period-correct costumes -- is given much more to do: She holds signs at political rallies, learns how to evade fellow spies (go into a "lady shop," because "no man will follow you in there"), and has passionate affairs with desperate men. Yes, it's all a lot quieter than most spy movies; there's nary a chase or a shoot-out, and one of the more dramatic moments of Red Joan involves a mink coat. Instead of explosions, there are conversations. And instead of murders, there are betrayals. But instead of easy answers, there are complex, nuanced questions, and a treat for a certain type of film watcher.