But as with “modern” mentions of Pepsi Free and a DeLorean in “Back to the Future,” these have aged into charmingly dated details of an innovative time-crossing thriller blending “Future’s” rush with “Backdraft’s” firefighting and a dash of “Zodiac.”
Neither man ever travels bodily from one era to another, thus eliminating the need to concoct some dubious deus ex time-machina like, say, the time-warping DeLorean hot rod of "Back to the Future."
There are a lot of "Back to the Future" moments - photographs with family members appearing and disappearing - and a healthy dose of "It's a Wonderful Life" moments as well - with family members either dying or being reunited after death in another timeline.
Frequency alternates between gripping and sentimental, suspenseful and clever, with disarming ease; the time-travel gimmick works because of its novelty, and because none of the characters can control it the way they would, say, the DeLorean in Back to the Future.
Of course, as anyone who has seen the Back to the Future movies could tell you, meddling with the past is bound to complicate things, and although you don’t need a degree in chaos theory to follow the rest of the story, it wouldn’t hurt.
Effective, too, are knowing touches reminiscent of the "Back to the Future" movies.