In this hospital there is a patient who has been causing a lot of trouble ever since they gave him a piano to use as therapy. He is Stefan Radetzky (Anton Walbrook), a Polish pilot who was shot down while fighting with the British Air Force, or so it is believed, but seeing as how he has lost his memory in the trauma it's hard to say. There is a woman with him as he randomly presses the keys, and she is urging him to return to the world, but as his doctors contemplate what to do next, they suddenly hear his most famous piece of music drifting from his room...
Stefan being a concert pianist, of course, in this major hit for wartime Britain which starred that debonnaire and dashing Viennese actor Walbrook who had come to the United Kingdom to escape the Nazis, and as he refused to play the evil German in propaganda movies, he was placed in a succession of roles which often had him playing sympathetic, Germans or otherwise. The fact that he was accepted in such movies, and indeed built up a very healthy fanbase among the Allies' cinemagoers, was testament not only to his talent but also that noble, oddly ethereal quality which made him such a magnetic presence.
Walbrook would receive his most lasting cult following with Michael Powell and Emeric Pressburger, The Life and Death of Colonel Blimp the most recalled of his wartime efforts (later, The Red Shoes did him a lot of favours too), but at the time Dangerous Moonlight was most celebrated, although a revisionism set in to tell you that it was the Warsaw Concerto which made the movie a hit. Produced by RKO's British arm, it had the pianist's favourite composition as the work which makes him much sought after, actually composed for the film by Richard Addinsell, and it's true that the recording of it sold very healthily off the back of its airing here. Northern Irish director Brian Desmond Hurst also made sure to appeal to as many audiences as possible with decent Americans and an amiable Irishman as Stefan's wry best friend (Derrick De Marney, a former Alfred Hitchcock leading man).
The plot is mostly made up of a lengthy flashback, for as the bombs begin to fall on London it triggers the clearing up of Stefan's amnesia as it all comes back to him, playing out before our eyes beginning with his first, very movie-movie meeting with his sweetheart, American newspaper reporter Carol Peters, who was portrayed by Sally Gray, a popular British star of the time whose promising career was scuppered by the nervous breakdown she had just after completing this film. She did make a return to the screen some years later once the war had finished, most memorably in the comedy thriller Green for Danger, but you can only wonder at how things could have turned out for her if she had been able to capitalise on her much-admired appearance here.
The lovers' encounter sums up the mood of the title, as she is attracted by the sound of his piano as the bombs fall on Warsaw, and in the moonlight they get to know each other, eventually meeting up again when unbeknownst to Stefan his fellow pilots voted to send him to safety in the United States where he will do fine work for the propaganda effort. This he does, but the pull of Europe is so powerful that he cannot resist it, which breaks up his relationship with Carol almost as if he has a death wish, determined to sacrifice himself if it means he can save the world from the Nazi threat. Needless to say, this was all swooningly romantic on a grand scale as well as the more traditional intimate one, and the footage of actual Battle of Britain skirmishes in the air lent it a vitality and authenticity that perhaps the stagier aspects did not. What saved it was the soulful nature of Walbrook as well as his character's theme tune in combination; it may have been propaganda when it came down to it, but it was effective.