Oooo, "Frequency" made me mad! There I was, completely engrossed in this eerie and intelligent, "Twilight Zone"-like time-shifting yarn -- one that gracefully sidestepped most of its inherent logical pitfalls and successfully embraced the sincere sentimentality at its core -- when suddenly, 20 minutes from the end, it downshifted into utter dimwittedness and puttered to an unforgivable, "Friday the 13th" finale.

Until it completely self-destructs in the last act, the picture is a clutcher in terms of both emotion and excitement. It's about an handsome, 36-year-old Queens cop named John Sullivan (Jim Caviezel) whose disconsolate life has been irrevocably shaped by the death of his firefighter father in 1969.

One night before the anniversary of the fire that claimed his pop, spectacular sun spot activity has been wreaking havoc on telecommunications -- just as it had the same night 30 years ago -- and John pulls out his dad's old ham radio, remembering how such storms boosted the signal.

Fiddling with knobs and levers, John somehow tunes in a signal that bridges time and soon realizes a friendly, familiar-sounding fellow he's contacted through the electromagnetic static -- this firefighter who talks about the 1969 World Series as if it's still going on -- is in fact his father. He has a chance to alter the past. He can save his dad's life.

Naturally, dad (Dennis Quaid) takes some convincing. But when he finds himself facing a warehouse blaze exactly as the stranger on the radio predicted, he takes John's advice and survives to radio back the next night for a cathartic father-son moment that sets the strong emotional tone for the whole film.

But this alteration of history has horrible consequences, some of which relate to an infamous crime spree that now invades the father's life when it originally had not.

Tightly directed by Gregory Hoblit ("Primal Fear"), "Frequency" is the kind of story that must be handled with limber precision, lest it become a ridiculous discombobulation of science fiction balderdash. For the majority of the film, Hoblit does a deft job holding such shash at bay.

His grasp on the audience's emotional state is strong enough that just seeing John's mother (Elizabeth Mitchell, "Gia") in a nurse's uniform ties your gut in a knot (for reasons I won't spoil here). He gets moving performances from Caviezel and Quaid (if you ignore his on-and-off Queens accent), and makes good use of Andre Braugher in a pivotal family friend role that spans both time periods (the aging makeup is some of the best I've ever seen).

He employs dream-like eruptions of sepia-toned, perspective-camera images to demonstrate how John's memory realigns itself with what he has changed in the past. He even tosses in an ambiguous aside about string theory and space-time to appease scientific nit-pickers (color me guilty).

The picture's relative complexity shows a refreshing confidence in the viewer, as John -- a homicide detective -- uses modern forensics to discover clues about the crimes in the past, in a desperate attempt to save lives.

But somewhere between reels four and five, "Frequency" becomes bloated with shopworn sci-fi and suspense gimmicks, force-fed into the script (by studio exec turned screenwriter Toby Emmerich) to add unnecessary titillation to what had begun as a relatively cerebral story.

In 1969, the father loses every shred of common sense while tracking the crime spree, becoming mixed up in the case in ways that are unforgivably stupid and trite. From this point on, "Frequency" gets subtly dumber and dumber, eventually jettisoning the picture's earnest tone, scuttling several simple, obvious and satisfying resolutions, and opting instead for a last act adrenaline rush of illogical and over-produced, cheap scares and shivers.

"Frequency's" downward spiral is such a tremendous slap in the face that it all but negates the sound, intelligent and engrossing first hour of the movie.