The 1889 Paris Exposition serves as the backdrop for this eerie mystery, in which English tourist Vicky (Jean Simmons) and her brother, Johnny (David Tomlinson), visit the fair and retire to their separate hotel rooms for the night. When Vicky wakes in the morning, not only is Johnny missing, but his entire room has vanished. Inquiring about her brother's whereabouts, Vicky grows increasingly disturbed when the hotel manager (Cathleen Nesbitt) insists that Johnny was never there at all.