Berlin-based David Pratt has just died from a fall off his apartment building's roof; it's unclear whether his death was accidental or a suicide. His wife, aircraft-propulsion engineer Kyle Pratt, and their 6-year-old daughter Julia Pratt are in emotional turmoil as they fly his body back from Berlin to New York for the burial. Aboard the Alto Airlines jumbo-jet flight, Julia goes missing while Kyle naps. Julia has a tendency to wander off so at first Kyle thinks this is just another instance and she'll be found easily, but she is proven wrong, and nobody remember ever seeing young Julia Pratt on board, including the flight attendants. As they look for her, the entire flight crew and Kyle learn that there is no record of her ever having been on board - no boarding pass, no name on the official manifest, and no extra person on the official head count conducted by the flight attendant prior to the supposed disappearance. Further information from Berlin comes to light: that Julia could never have been on board. Kyle is certain that someone on board has taken her and that someone with the airline who could alter official flight records is also involved in her disappearance. Kyle's increasing rantings put her at direct odds with the inconvenienced passengers, the flight attendants (who previously admitted that they have their favorite and not-so-favorite passengers, and now Kyle is in the latter category), and, most specifically, Captain Rich and Sky Marshal Carson, whose foremost goal is the safety of all passengers. With a detailed knowledge of aircraft design, Kyle believes she has an upper hand in finding Julia if only someone would believe her and let her search. Or is the trauma from David's death playing games with her mind so that she's searching for someone who no longer exists....or ever did?