The short review is 'don't bother buying the DVD or streaming it - it's a bit rubbish'. Let me elaborate.
To bo honest, I only bought this because Judi Dench is in it. I was vaguely aware of the story of Melita Norwood, around whom the storyline is loosely based, and that should have been the warning I needed.
In essence, this film glorifies the betrayal of one's country. It glorifies and tries to humanise someone who was, to all intents and purposes, a traitor. Oh, she did it for the best of reasons is the subliminal message which the viewer is constantly assailed with during this almost two hours of dirge.
Judi Dench is as ever quite brilliant but wasted amid a cast of mediocrities. The acting of virtually all the other characters is uniformly wooden or over the top. Just about every stereotype about the 1940s is there for all to see.
Perhaps the most laughably appalling performance is from Tom Hughes who plays Prince Albert in Victoria. Indeed, he played exactly the same character here, replete with the German accent. I half expected Queen Victoria herself to appear at some point. He is supposed to be an actor. Could he not have fashioned a unique character to play here? He even had the same foppish haircut, although the moustache was noticeable by its absence.
The second most wooden performance goes to Ben Miles who played Joan's son, Nick. He was utterly brilliant in Coupling and The Crown, where he played Group Captain Peter Townsend, but here, well, not so much. Where he wasn't wooden, he committed the cardinal sin of overacting. In short, his character wasn't believeable. Perhaps we should forgive him a little given he didn't write the appalling script his character had to follow.
If you give state secrets to a foreign power you are a traitor to your country. Nothing can twist that basic fact, yet this film tries to make out that it was a noble cause that Joan was embarked upon. She wanted to level up the nuclear weapons playing field. It even makes out she was the one responsible for the concept of mutually assured destruction.
The authorities and the establishment are portrayed as the bad guys here. No. The only villain in this film is Joan herself. Or Melita Norwood. Norwood was never prosecuted for her treasonous betrayal due to her age. Perhaps she might have had cause to think that were the boot on the other foot and she had been a Russian citizen, what fate might have befallen her at her ripe old age had she been found to have betrayed her country and handed its secrets to the West.
I doubt whether it ever crossed her treasonous mind.