This is a cleverly constructed thriller featuring an on form Jean Simmons as the naive girl holidaying with her brother "Johnny" (David Tomlinson) in Paris at the time of the Great Exposition. Things take quite a mysterious turn on their first morning when not only has her brother disappeared - but so, too, has his hotel room! In the best tradition of "the Lady Vanishes" (1938), nobody in the hotel - staff or guest - recalls ever having seen him and she is widely suspected of being either mad, or just a chancer hoping to avoid paying her bill... It is only the timely intervention of Honor Blackman's ("Rhoda") who attempts to return fifty francs that her friend "George" (Dirk Bogarde) borrowed from the missing man the night before, that she begins to get her head together and enlisting painter "George" to help, they must get to the bottom of things. Aside from the ending, which is poor in the overall context of the film, this is a good looking, well paced drama with a good cast, decent writing and some lovely Parisian scenarios to maintain the intrigue well. Simmons plays her part mixing the initial joy and enthusiasm of a young girl in Paris with that of the sister terrified for her brother, and for her own sanity really well. It is well worth a watch, this one.