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.
Archer and the crew of Enterprise find themselves in 1944 and discover the outcome of World War II was altered by the Temporal Cold War.
With Silik's help, Archer searches for the temporal operative who altered Earth's past and threatens to destroy all of time.
Enterprise returns to Earth to a hero's welcome, Archer is haunted by his experiences and actions in the Expanse.
Criminal Arik Soong is brought aboard Enterprise to assist in finding some genetically enhanced humans he created after stealing altered DNA left over from the Eugenics Wars.
Soong returns to Cold Station 12 with the Augments, a medical facility where he once worked, where there are hundreds of genetically engineered human embryos stored.
After turning on their creator, the Augments attempt to start a war between Humans and Klingons.
Earth's embassy on Vulcan is bombed and the evidence points to a religious faction known as "Syrrannites," a group following a revolutionary interpretation of the teachings of Surak, the father of Vulcan logic.
Archer and T'Pol locate the Syrrannites. However, unbeknownst to Archer and T'Pol, more is going on than just a simple act of terrorism.
Archer, T'Pol and T'Pau attempt to take a sacred, but controversial artefact back to the Vulcan High Council, in hopes of settling an internal struggle going on among the Vulcan people.
The inventor of the transporter, Emory Erickson, comes aboard Enterprise for a risky experiment.
Non-corporeal aliens study the Enterprise crew as they respond to a fatal viral infection brought on board from an away mission.
Enterprise journeys to Babel with a Tellarite ambassador on board for peace talks with the Andorians, when a distress call from Shran is received.
Archer tries to unify the Andorians, Tellarites and Vulcans in a plan to capture a marauder ship threatening to destabilize the region.
Archer visits Shran's icy homeworld to find an Andorian subspecies called the Aenar, to determine their connection to the marauder destroying ships in the region.
While Enterprise visits Earth for the launch of Columbia, Phlox is kidnapped and forced to help the Klingons deal with a grave threat to their species.
With Columbia's help, Enterprise's crew grapples with sabotage to their ship as they pursue the truth behind the kidnapping of Phlox.
As a gift for negotiating with the Orion Syndicate, Captain Archer receives three Orion Slave Girls. Soon, their seductive powers begin to affect everyone on board except for Trip and T'Pol.
In the mirror universe, Commander Archer mutinies against Captain Forrest in order to capture a future Earth ship found in Tholian space.
In the mirror universe, Archer commandeers the 23rd-century Defiant from the Tholians and uses it in a nefarious power grab.
A xenophobic faction of humanity threatens to undermine talks to form a new coalition of planets.
A human isolationist leader threatens to destroy Starfleet Command unless all aliens leave Earth immediately.
Commander William Riker of the Enterprise-D is torn between his loyalty to Captain Picard and his duty to a former captain.