Jack Mayland has spent a lifetime asking himself the same question over and over. What if? What if his little sister had not died as a child? What if his parents had not divorced after the incident? What if the entire course of his life had not been derailed by that one tragic accident? And what if there was a way to change it all and get his life back on track.

A chance encounter with the brilliant and controversial psychologist Dr. Jennifer Melton gives him hope he may finally get some answers. The doctor has plenty of regrets about her own life, but she believes she has discovered a way to travel back into one's own past and change a single event causing a ripple effect that can alter the present.

Jack agrees to participate in the study, but after several failed attempts, he begins to have doubts about the whole project. A new relationship with the doctor's enigmatic assistant Rebecca, gives rise to a whole new set of questions. What if it's all an illusion, a trick of some kind? What if the doctor is just manipulating him, using him for her own selfish reasons? What if the past really can't be changed at all?