The fourth and final season of Star Trek: Enterprise helped bridge the gap between Enterprise and the future developments of Star Trek: The Original Series. Capt. Archer and his crew escape from an alternate timeline — the result of the continuing Temporal Cold War — in which the Nazis have invaded U.S. soil in 1944. In the normal Enterprise timeline, political upheavals have left relations between Vulcans, Andorians, Tellarites, and Humans in a state of near-disastrous chaos.
The main story arcs for Season 4 include the trilogy ("Borderland," "Cold Station 12," and "The Augments") in which Dr. Arik Soong (played by Next Generation alumnus Brent Spiner) and his superhuman "Augments" chart a tragic course that would lead, in future generations, to the creation of Spiner's cybernetic NextGen character, Data. Another three-episode arc, "The Forge," "Awakening," and "Kir'Shara," returns T'Pol (Jolene Blalock) to her native Vulcan, where encounters with the legendary philosopher Surak and a zealous sect called the Syrannites lead to pivotal history with the Vulcan High Command. In subsequent episodes, Phlox (John Billingsley) discovers the reason why some Klingons lack "cranial ridges," and "In a Mirror, Darkly" marks an eventful return to the "Mirror Universe" from the original series episode "Mirror, Mirror" and the reappearance of the U.S.S. Defiant from the original series episode "The Tholian Web."