Grade: C

From a writer’s perspective it must be terribly frustrating to come up with an intriguing premise and then find you’ve got nowhere to go with it. That’s what’s happened to Gerald Di Pego (“Phenomenon,” “Angel Eyes”) in “The Forgotten.” A young mother distraught over the death of her nine-year old son in a plane crash is suddenly informed by her husband and her psychiatrist that she never had a son at all–that she’s imagined the entire history of the child; and to add to her anguish, nobody else remembers the boy, either. But she’s certain that everyone but her is wrong, and that somehow her son has been “erased” by some mysterious force. Is she right, or merely unbalanced? If the former, how was it done–and by whom, and why? If the latter, can she be cured?

That’s a pretty good starting-point for a psychological thriller, and for the first twenty minutes or so of “The Forgotten,” it’s handled pretty well by Julianne Moore as the troubled housewife Telly Paretta, Anthony Edwards as her concerned husband Jim, and Gary Sinise as Telly’s psychiatrist; and talented helmer Joseph Ruben is quite successful in creating an atmosphere of vague dread. (Indeed, this might be thought of as the latest installment in Ruben’s series of “family” thrillers, following “The Stepfather,” “Sleeping With The Enemy,” and “The Good Son.”) But it’s not long before the movie goes way off track, turning into a silly shaggy-dog story that even a slick production, canny direction and a fine cast can’t rescue from absurdity. By the time it reaches its ludicrous conclusion, the story has come to resemble something fashioned from the “reject” pile of old “X-Files” scripts. (Moore even resembles that show’s Gillian Anderson.) You may find yourself gasping, but it will be from laughter rather than fear.

The crux of the plot that Di Pego constructs is that Telly quickly connects with another parent in the same situation as she–Ash Correll (Dominic West), who lost his daughter in the plane crash that killed her son but no longer recalls her at all. Telly’s intervention restores Ash’s memory of the girl, and soon they’re working together to uncover the truth about their “lost” children–a quest that finds them pursued by a variety of government types from the NSA, as well as by a NYPD detective (Alfre Woodard) who increasingly suspects that they might be on to something. Lurking in the background is a mysterious stranger (Linus Roache) who’s watching the duo’s every move–and may just be the key to the entire bizarre business.

“The Forgotten” has a lot going for it. Moore is a wonderful actress, and she invests even this part’s cliches with unexpected depth. Nobody else in the cast quite matches her, but West, though saddled with a stock alcoholic backstory, makes a satisfactory partner, while Edwards, Sinise and Woodard bring their customary authority to relatively small parts and Roach is, up until the ridiculous last act, suitably enigmatic. In addition, Anastos N. Michos’ cinematography, apart from a tendency to lurch periodically into hand-held mode, is nicely moody, and James Horner has contributed a score that cleverly mixes gentle fantasy-like melodies with more bombastic action-movie music. But before the halfway point the picture has degenerated into a rather dopey chase flick, and though Ruben tries to maintain the tension level, it pretty much runs out of gas before revving up for a flamboyant finale with a feel-good concluding twist. But even that ending is oddly unsatisfying: Telly’s husband is curiously absent from the equation, and she’s left sitting beside Ash with the clear suggestion that romantic feelings remain with them as a result of their experience together.

By that time, however, you’re not likely to have any similarly affectionate feelings toward the picture. With respect to “The Forgotten,” you’d be wise to do what poor Telly can’t about her son: put it out of your mind.