This is a sinister post-war drama with a terrible ring of sadness and tragedy about it, as the murderer is himself unaware of the fact that there is no ground for his motive. It's a tragedy of treason, and no one understands anything about it until it's too late.
This is therefore very much a film of mysterious undercurrents, understatements and hidden meanings, a film "written between the lines". It's easy to dismiss it for its failure to convey it's true meaning, but you do it wrong if you don't give it a lot of afterthought.
The surviving members of an underground resistance group against the Nazis meet annually in an old mansion outside London to commemorate their leader who was shot on that day by the Nazis. It appears that someone in the group had betrayed him. The new leader colonel Price, played by Donald Wolfit in a typical role of his, announces his decision to find out who the traitor was among them at their new meeting, and no one is allowed to leave the place until the issue is settled. An agent is on his way from Berlin to reveal the name. He never reaches them alive, and two American intelligence officers come importuning at their meeting to make matters worse and more complicated.
Donald Wolfit is a sure name to make any film he participates in a most memorable event. Christopher Lee as the doctor attracts all suspicion from the audience by his covert attitude as of a man who knew too much. Anton Diffring as the pianist contributes with the mood by his music, which he wants to call "Prelude to Death" which is altered to "Prelude without a name" by those who want to live. It's very reminiscent and almost a paraphrase of the Warsaw Concerto, it certainly brings the same atmosphere but is less efficient as music, while the drama story here is much more interesting and goes deeper. It's the difference between before the war and after.
At the same time it's a very intriguing murder thriller on the level with Agatha Christie, but here everything is logic and natural, it's a matter of inevitable tragedy of fate and not at all an artificial intrigue, like commonly with Agatha Christie.