Thirty years after his fireman father, Frank (DENNIS QUAID), was killed in the line of duty, thirty-six-year-old John Sullivan (JIM CAVIEZEL) is a detective who, along with his partner, Satch (ANDRE BRAUGHER), is investigating a previously unsolved, decades old serial murder case that's just been reopened upon the unearthing of the skeleton of one of the past victims.
Despite what sounds like a promising and rewarding career, John's life has been in near constant turmoil since his father's death. All of that's about to change, however, when his childhood friend, Gordon Hersch (NOAH EMMERICH), and his son come by for a visit and find Frank's old ham radio. With a recent flare-up of the aurora borealis, the signals end up traveling a long distance - all the way back to 1969 -- and John suddenly finds himself talking to his father in that year.
Once the two realize and then accept what's happening, they not only catch up on old - and new - times, but John realizes he can save his father's life since he knows when and how Frank perished. While eventually successful at that, John then realizes that their actions have changed another aspect of the past.
With the number of murders from that past serial case suddenly increasing, John realizes that they've done something that allowed the 1969 killer to continue his spree. From that point on, John and Frank team up as a set of long distance partners and try to stop the killer, although every action they take creates another change in the future and threatens their and others' safety, including that of John's mother, Julia (ELIZABETH MITCHELL).