Good science fiction thrives on innovation, and not every SF saga has to follow established rules.
According to an old convention of time-travel stories, for instance, even a tiny alteration in the past can affect the future in drastic ways. A writer can change this notion, but there should be a good reason, and the story should indicate why its rules are different from the ones obeyed by previous tales.
Frequency, the new SF fantasy from director Gregory Hoblit, waters down the time-travel rules for reasons that are all too apparent.
The movie's main interests aren't the fascinating paradoxes of time travel at all, but the thrills and chills of ordinary melodrama. Although the plot has a science-fiction premise, this only sets the stage for a story oscillating between family sentimentality, on one hand, and the violence of a serial-killer manhunt, on the other. These are reliable box-office commodities, so the picture may do well financially. But science-fiction buffs won't find much here to broaden their horizons.
The main characters are Frank Sullivan, a New York City firefighter, and police officer John Sullivan, his son. Tinkering with an old ham-radio set one evening, John finds himself in contact with the last person he would have expected: his father, Frank, who died years earlier in the line of duty.
Realizing that they've entered a radio-wave time warp - the cause turns out to be a magnetic storm on the sun - they make the most of the occasion, with John telling Frank how to avoid the accident that's due to kill him.
This alters their family's past in profound ways: Frank survives the deadly fire, and John finds his mind flooded with new memories of their additional years together.
But history has changed in negative ways too, putting the life of another loved relative on a collision course with a demented murderer.
Burning up the airwaves with their radio hookup, John and Frank join forces across the years to track down the killer, and deepen their own relationship in the process.
"Frequency" builds a fair degree of suspense in its sometimes violent crime sequences, and many viewers will shed a tear over the family affection that John and Frank share during their gradual progress to a genuinely sweet finale.
But while family values are the film's strongest emotional suit, a single-minded emphasis on them weakens the story's underlying logic.
Frank and John make enormous changes to the past events of their lives, and all the effects of these alterations revolve around their own domestic situation, as if the rest of New York - even the rest of the planet - were a mere backdrop to their household.
A more sophisticated yarn would pursue its time-warping possibilities in less restricted directions, tying the fate of one family to the larger world around it.
"Frequency" is warm and endearing, but it could have been a great deal more.
*Rated PG-13; contains violence.
(c) Copyright 2000. The Christian Science Publishing Society