Season 4
Upon returning home after preventing a second Xindi attack, Enterprise explores cultural shifts on Vulcan; forges alliances with Earth's neighbors in the face of Romulan aggression; deals with a plague inside the Klingon Empire; explores the Mirror Universe; and overcomes xenophobic elements to lead an interstellar community.
Episodes
1. Storm Front (1)
Archer and the NX-01 find themselves in Earth's past, with events of World War II altered by the Temporal Cold War.
2. Storm Front (2)
With Silik's help, Archer hones in on the temporal operative who altered Earth's past and threatens to destroy all of time.
3. Home
Once the NX-01 finally returns to Earth, the weary crewmen face repercussions of their journeys, both positive and negative.
4. Borderland (1)
When genetic supermen left over from the Eugenics Wars hijack a Klingon ship, Archer must rely on their creator, the criminal Dr. Arik Soong, to help hunt them down.
5. Cold Station 12 (2)
Arik Soong leads his band of Augments to a medical facility where hundreds of genetically enhanced embryos are still stored, intending to retrieve them and bring them to life.
6. The Augments (3)
In defiance of their "father," Arik Soong's Augments devise a heinous plot against the Klingons which will surely lead to interstellar war.
7. The Forge (1)
Earth's embassy on Vulcan is bombed, and the ensuing investigation puts Archer and T'Pol on the trail of a Vulcan religious faction hiding in a treacherous desert.
8. Awakening (2)
Archer and T'Pol encounter the Syrrannites, a radical group hiding in the Vulcan desert, while the NX-01 crew contends with Vulcan power ploys.
9. Kir'Shara (3)
Archer, T'Pol and T'Pau attempt to bring the Kir'Shara — an artifact believed to contain Surak's original writings — to the Vulcan capital, as the NX-01 gets involved in a Vulcan-Andorian military clash.
10. Daedalus
The inventor of the transporter, Emory Erickson, comes aboard Enterprise for a risky experiment.
11. Observer Effect
Non corporeal aliens study the Enterprise crew as they respond to a fatal viral infection brought on board from an away mission.
12. Babel One (1)
Enterprise journeys to Babel with a Tellarite ambassador on board for peace talks with the Andorians, when a distress call from Shran is received.
13. United (2)
Archer tries to unify the Andorians, Tellarites and Vulcans in a plan to capture a marauder ship threatening to destabilize the region.
14. The Aenar (3)
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.
15. Affliction (1)
While Enterprise visits Earth for the launch of Columbia, Phlox is kidnapped and forced to help the Klingons deal with a grave threat toward their species.
16. Divergence (2)
With Columbia's help, the Enterprise crew grapples with sabotage to their ship as they pursue the truth behind the kidnapping of Phlox.
17. Bound
As a gift for negotiating with the Orion Syndicate, Captain Archer receives three Orion Slave Girls.
18. In a Mirror, Darkly (1)
In the mirror universe, Commander Archer mutinies against Captain Forrest in order to capture a future Earth ship found in Tholian space.
19. In a Mirror, Darkly (2)
In the mirror universe, Archer commandeers the 23rd-century Defiant from the Tholians and uses it in a nefarious power grab.
20. Demons (1)
A xenophobic faction of humanity threatens to undermine talks to form a new coalition of planets.
21. Terra Prime (2)
A human isolationist leader threatens to destroy Starfleet Command unless all aliens leave Earth immediately.
22. These Are the Voyages...
Six years in the future, an emotional Captain Archer and the crew return to Earth to face the decommission of Enterprise and signing of the Federation charter.