May 1889. Like many others, young-adult siblings Johnny and Victoria Barton, British nationals who have only each other in the world, have arrived in Paris, traveling from Naples via Marseilles, for the World's Exposition. While Victoria is a bundle of excitement about their 48-hour stay in Paris, to include the opening day of the Exhibition, Johnny is preoccupied by all the logistics of their extended vacation. The one day changes 180 degrees when first thing in the morning, Victoria cannot only not locate Johnny, but there is no indication that he was ever at their hotel. The hotel owner Mme. Hervé, her brother Narcisse the front desk clerk, and bellboy who waited on them deny that anyone accompanied Victoria to the hotel, his name is not in the hotel register, and even his hotel room, number 19, has totally disappeared--Mme. Hervé shows Victoria that room 19 is only a lavatory. Beyond speaking to the British Consul and the police, who can do nothing to help her until she comes up with some proof that Johnny not only exists but was accompanying her, a panicked Victoria tries to find anyone, especially at the hotel, who can corroborate that Johnny was with her. She might have found that someone in George Hathaway, a fellow British national living in Paris eking out a living as an artist; friends of his are also staying at the hotel for the Exhibition. Victoria and George together try to discover exactly what happened to Johnny and why Mme. Hervé and others at the hotel are lying about his existence.