I will give it a generous 3/10 for a reasonably authentic depiction of an early 1950s British seaside town, comparatively untouched by war. But it did feature at least one modern electrical fitting!
It's curious that one review of last week's item vociferously contended that "England" was not involved in the Cold War. Maybe this was from a very young person with absolutely no grasp of history, and possibly an American, due to the blatant inability to understand the difference between England and the UK. But the UK was very much involved, and fear of nuclear annihilation was something we all lived with on a daily basis. The term 'Cold War' is attributed to George Orwell, born in British India, but very definitely an English writer. He coined it in a 1945 essay, and as members of NATO and close allies of the USA, the UK was a prime target for Soviet nukes, especially with a great many US air bases on its soil. I was there as a child, and I clearly remember 1952. The Civil Defence Corps was set up by the UK government in 1949 to actually prepare the citizens for nuclear war, which seemed inevitable.
However, I don't feel that this production evokes the cold war atmosphere in any true sense. It could be a spy thriller set against any historic background, rather than the 'Mutually Assured Destruction' (acronym MAD!) of that era in Britain.
David Walliams is again wooden. Maybe he should stick to comedy. Jessica Raine manages marginally better, but was more convincing as a young midwife with a heart of gold. James Fleet brings his absolute dimwittedness of 'Vicar of Dibley' to this series, when he is meant to be a very clever MI5 spymaster.
I have never read these Agatha Christie stories, but imagine that they are far better in print than this poor half-hearted effort.