The original plot comes from a novel of the same name,[2] set in what was then the mysterious world of radio in what was then the BBC's new broadcasting centre, Broadcasting House. It was written in 1934 by Val Gielgud – brother of John Gielgud and at that time the BBC's Head of Productions – and "Holt Marvell" - actually Eric Maschwitz, a lyricist and writer for films and the BBC.
Film
In the same year, it was made into the film, directed by Reginald Denham, with Ian Hunter (best known as King Richard I in the 1938 Adventures of Robin Hood) as the detective, Donald Wolfit as the murder victim, and Val Gielgud himself as the drama producer, Julian Caird. The film sticks closely to the plot of the book, but is lighter in tone, and capitalizes on the glamour of broadcasting by including a number of cameo appearances by radio stars, among them Hannen Swaffer, Gillie Potter, Elisabeth Welch and Percival Mackey. During the investigation, the detective uses a recording of the radio programme during which the murder occurred, and he refers to the "Blattnerphone", one of the first sound-recording machines, and one of which had actually been installed at Broadcasting House in March 1932.
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