The mystery plot that was used to such advantage in "The Lady Vanishes" and "Sorry, Wrong Number" has reappeared with somewhat less success in "So Long at the Fair." The plot common to these films involves a heroine who suspects a crime that no one else will believe was committed. In "So Long at the Fair" a young English girl, in Paris for the 1889 exposition, checks into a hotel with her brother. She awakens the next day to find that not only her brother, but his room has disappeared, and that no one in the hotel has ever heard of him. The success of this plot's earlier examples was due largely to the suspense and hopelessness of the heroine's situation, which are missing in this one. Somehow one can't avoid feeling that the girl's artist-boy-friend will come up with the solution sooner or later.

What the film lacks in mystery it makes up in other ways, particularly the performance of Jean Simmons, who gives a fascinating exhibition of mid-Victorian beauty and charm. The Rank Studios seem to have hit on a laudable policy of casting first-rate actors in supporting roles. This, together with the skillful contrast between the mystery and the gay exposition background, add considerably to the film's quality.