The story is set in a distant future where humanity is locked in a protracted conflict with the reptilian alien species known as the "Sirians." To gain an edge in the war, the military employs a team of scientists to develop a device capable of predicting future events with precision.However, when a "variable man" named Thomas Cole accidentally arrives from the past, he disrupts the scientists' plans. Cole's presence introduces an element of unpredictability that the rigidly deterministic scientists struggle to reconcile with their deterministic worldview. As Cole becomes embroiled in the war effort and forms relationships with the people he meets, he challenges the notion of predestination and the idea that the future is set in stone.