Jodie Foster has that rare actor's quality of being transparent to the camera, an ability that lets us see inside her brain as she's confronted with a conundrum or mystery - in the case of her new film "Flightplan" the bizarre disappearance of her six-year-old daughter from the seat next to her on a plane at thirty-seven thousand feet.

This is not to say that Foster cannot create a character from scratch and make us believe in that person; we need go back only as far as her last film, "A Very Long Engagement," to recall her as the beautiful Elodie Gordes, a woman faced with an impossible choice, played, in impeccable French, with passion and bravery.

"Flightplan,"a much better film than the similar "Panic Room" of 2002, puts her on board a flight heading home from Berlin with her daughter and the coffin of her husband, who fell from the roof of their building just a week before. A few hours into the flight she wakes from a nap to find her daughter missing; no one on board can recall seeing her, and as the film progresses from casual search of restrooms to frantic confrontations with the crew we are as mystified as she is - because there is no record of the little girl on the plane's manifest.

I won't spoil this for you; for the first hour "Flightplan" is a brilliantly constructed locked-room mystery - you know, no one can get in or out and yet…. Should we believe her? After all, where could the child go? Foster's character is given to us as a propulsion engineer who worked on the design of this very plane; she knows it inside and out. But is she hallucinating? At the very beginning of the film we've seen her talking with her dead husband, so how far can we trust her? The writers, Peter A. Dowling and Billy Ray, and the director, Robert Schwentke, never allow the film to go over the edge into melodrama; every confrontation, every ratcheting up of tension is carefully laid out for us. The captain (Sean Bean) acts correctly and sympathetically in the face of an impossible situation; the air marshal on board (Peter Sarsgaard) is understated and correct.

And so we are carried along for an hour in the hands of experts - the writers, the director and the actors. And then - with 30 minutes still to go, the film gives itself away and reveals the truth. It is a terrible mistake, because this is the kind of mystery that must hold its secrets until the final moments, when we and the protagonists solve the mystery together. Instead, the tension is suddenly shifted to a mano-a-mano between two people - and the outcome is foreordained. The suspense has oozed out of the film - needlessly - and we now just sit and wait for the ending.

Nevertheless, "Flightplan" has the requisite structure, the superb acting, and the power to compel our complete attention. Though Foster has played this character before, she finds wonderful ways to make it feel new; it is a pleasure to see such a good actor working at the top of her form.