The Forgotten (2005)

This movie starring Julianne Moore started off like gangbusters with an intriguing premise -- she plays a mother whose son was killed in a plane crash about a year earlier and she continues to grieve.  However, slowly, proof that the son ever existed ceases to be available as his image disappears from family photographs and videos and as even her therapist, best friend and husband deny that there ever was such a person.  Since she is a decent actress, one identified with her plight and wondered where the story was going.  Then about two-thirds the way through came a plot development so far our of left field that my mouth was literally agape.  After that it just became more and more unbelievable as my flabber was ghasted, and by the end I couldn't care less.