Dame Judi Dench again provides an acting masterclass in this British period romp about a British physicist who leads a double life, spying for the KGB.
The story begins in London in 2000 when Joan Stanley, a retired librarian in her 80s, is arrested by M15 for treason. The death of a previous colleague has revealed her to be one of the longest-serving double agents in Britain - a suggestion that stuns everyone, from Joan's neighbours to her lawyer son.
It's an interesting starting place for a story; spies aren't always James Bond-esque, they can also be your lovely, sweet, perfectly ordinary neighbour.
Joan's story is told in flashbacks, as she's questioned by government officials. First, as a student at Cambridge, and then as a young physicist employed as a secretary at the British Non-Ferrous Metals Research Association in London during World War II.
It's here that Joan, played in her younger years by Sophie Cookson, is exposed to top-secret atomic-bomb information that she's accused of leaking to the USSR.
Dench gives a beautifully nuanced performance. At first she plays to perfection the part of a confused and innocent octogenarian then, as the story unfolds, she slowly reveals a woman who felt a moral obligation to leak secrets to the Soviets, believing both superpowers having the technology would prevent them from annihilating each other.
Cookson gets the less meaty role. It's hard to know whether this intelligent young woman was a communist sympathiser or just fell for charismatic socialist and spy Leo (Tom Hughes), with Joan's university years and time working in London reduced to a melodramatic romance.
The result is a story that could have been thrilling but is instead a nice, repetitive and slightly dull period costume drama. Thank goodness for Dame Judi Dench.
Judi Dench, Sophie Cookson
M (Sex Scenes)
A handsomely shot but dull spy thriller.