So Long at the Fair (1950)

"Paris ! ... city of love and intrigue ... scene of the most fascinating mystery ever filmed !"

Vicky Barton and her brother Johnny travel from Naples to visit the 1889 Paris Exhibition. They both sleep in seperate rooms in their hotel. When the she gets up in the morning she finds her brother and his room have disappeared and no one will even acknowledge that he was ever there. Now Vicky must find out what exactly happened to her brother.