An awful tragedy disrupted the otherwise peaceful life of Jim Morris, a repairman at a roofing and siding company in Missouri. His young daughter, Ruth, died after being hit by a car when she ran into the street to chase after a ball she had thrown to the family dog. Jim tries to cope with his grief, but the grief, along with the regret about what he had been doing just before Ruth had been hit, haunts him. Odd changes, however, begin to occur at Jim's company. A young man named Mike, fresh from high school, gets a job there. Young Mike is more than he seems. He is a reversal engineer who specializes in changing the past. Mike's scientific expertise allows him to change past circumstances so that Ruth does not die, but reversal engineering is a new scientific discipline and Mike has yet to work out all of the glitches. Changing one circumstance often leads to a breakdown in others. Can reversal engineering be refined so that Jim's wish to have his daughter back comes true without consequences? Or, will this new technology actually make matters worse?