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.