As the film begins, a man uses laser-sighted submachine guns in the year 1863 to rob gold bullion from Confederate soldiers. In the next scene, set in 1994, top government officials create the Time Enforcement Commission (TEC) to combat misuse of the new discovery of time travel. Senator Aaron McComb volunteers to oversee the commission. Shortly afterward, police officer Max Walker is offered a job as a TEC agent, and shortly after the job offer, he is attacked by intruders at his suburban home. During the attack, Walker's wife Melissa is killed in an explosion.
Ten years later, Walker is an experienced TEC Agent. When he is sent to 1929 to arrest his former partner Atwood (Schombing) for taking advantage of the U.S. stock-market crash, Atwood reveals that he is working for McComb, who needs money for his U.S. presidential campaign. Terrified of McComb, Atwood tries to kill himself by jumping out a window. Walker catches him and takes him back to 2004, but Atwood refuses to testify against McComb and is sent back to 1929 where he falls to his death. Haunted by his memories of Melissa, Walker vows to stop McComb.
Walker is then sent with agent Fielding (Reuben) to 1994 where they find a young Senator McComb arguing with his partner Jack Parker about their company's new computer-chip technology. Parker offers to buy McComb's share of the company, but an older McComb arrives from 2004 to warn the younger McComb that the chip will make huge profits. A fight ensues when Walker is double-crossed by Fielding, who works for McComb. McComb kills Parker and escapes back to 2004.
When Walker returns to 2004, things have gotten worse: The TEC is being closed, McComb owns the computer company and is a powerful political figure, TEC director Matuzak (McGill) is no longer Walker's best friend, and the TEC staff have no memory of McComb's actions in 1994. Realizing that he must act immediately, Walker commandeers the time machine with Matuzak's help.
Back in 1994 again, Walker finds Fielding recuperating from gunshot wounds in a hospital. In the lab, he finds a sample of Melissa's blood indicating that she is pregnant, remembers that her death occurred on that day, and decides to rescue her. After finding Fielding murdered, he goes to the shopping mall where he and Melissa met before she died, finds her, and explains who he is.
In the final showdown, McComb's thugs arrive at the Walker home as they did at the beginning of the film, but this time the older Walker is waiting for them. The two Walkers defeat the thugs with Melissa's help. Melissa and the young Walker are wounded, and McComb takes Melissa hostage and sets a time bomb to kill them all, but the young McComb appears, tricked by a message from Walker. According to the film, two instances of the same matter cannot occupy the same space at the same time (compare to the Blinovitch Limitation Effect). Therefore, when Walker pushes the younger McComb into the older one, the two McCombs fuse into a writhing, disappearing mass of blood and flesh.
Walker carries Melissa out of the house just before it explodes. When he returns to 2004, the world is less corrupt and McComb has not been seen since he vanished ten years earlier. At home, Walker finds Melissa and their son waiting to greet him.