Not many people know that the basic plot of this film is based on a real life event that took place during the 1889 Great Exhibition in Paris. There are major differences of course; for a start, the young woman arrived with her mother and not brother as depicted in the film. Secondly, they arrived directly from India and not Italy. Ironically, the 1955 TV Episode 'Into Thin Air' - part of Alfred Hitchcock presents - is far closer to the truth than the 1950 feature film.
But I agree to the change of plot because casting the missing person as the brother gives the story more flexibility. That said, the script should have been far more exciting than the rather bland fare that the director had to cope with. There was plenty of scope for a brilliant thriller with plenty of red herrings, something which Hitchcock would have exploited with glee - as he already had done in his 'The Lady Vanishes' and would do so again in the aforementioned TV episode.
But I agree to the change of plot because casting the missing person as the brother gives the story more flexibility. That said, the script should have been far more exciting than the rather bland fare that the director had to cope with. There was plenty of scope for a brilliant thriller with plenty of red herrings, something which Hitchcock would have exploited with glee - as he already had done in his 'The Lady Vanishes' and would do so again in the aforementioned TV episode.