Dench portrays the elderly Joan Stanley in the present day. She has retired from her position at the British Non-Ferrous Metals Research Association and is the mother of Nick (Ben Miles, Ninja Assassin. Back in 1938, young Joan, then known as Joan Smith (Cookson), was a physics major at Cambridge University. It was during this time that she became friends with Sonya Galich (Tereza Srbova, St Trinian's and the latter's cousin Leo (Tom Hughes, About Time). Sonya and Leo were agents working for Comintern. Meanwhile, Britain was hurtling into another world war and the pressure was on British scientists to develop an atom bomb before the Germans could come up with one. Similar weapons were also sought by Moscow.
Much of the story is told in flashbacks when Joan is being interrogated by officers from the Special Branch after she has been exposed as a Soviet mole. Joan's position as the personal assistant to Dr Max Davis (Stephen Campbell Moore, Goodbye Christopher Robin) gave her pretty much-unfettered access to classified material concerning nuclear research, which she passed to the Soviets. Her motives were unique as most double agents usually do it for money. Instead, Joan sought to level the playing field in the belief that if both the British and the Soviets had the same type of weaponry, they would be hesitant to use them on each other as the consequences would be horrendous. After she is outed, a heckler on her front lawn holds up a placard with the words "RED JOAN", hence the title of the film.
Dench's role in Red Joan is the opposite of her usual role in the James Bond films, in which she plays M, whose job is to weed out traitors. Srbova exudes charisma as Sonya, who eventually gets Joan to turn following the surrender of Japan and the conclusion of the Second World War. The narrative deftly weaves in major events in modern history. The slow-burn effect is deliberate, but may be considered boring by those who are not history buffs.
On the whole, Red Joan appeals mainly to aficionados of British drama. The polished accents of the characters capture the spirit of the 1930s, giving the movie an old-school charm. Both Dench and Cookson slip easily into character, tugging at the heartstrings of the inner leftie in us.