This list of Star Trek: Enterprise episodes is accompanied by each episode's original airdate on UPN in the United States, along with its Nielsen rating, and number of viewers.
When viewing the ratings and numbers, it should be kept in mind that UPN does not have coverage in all regions of the United States; in many areas, the show is aired on other broadcasters at times that are not covered by the ratings.
UPN itself also shows a weekend rebroadcast of each episode which is not rated.
The network has also been criticized for allowing affiliates to preempt many episodes of the series for local programming.
All these factors have been blamed for the show's dipping ratings.
UPN cancelled the series on February 2, 2005, but it will be allowed to complete its fourth season, with the final episode expected to air in late May.
The four seasons of Enterprise are scheduled to be released on DVD in North America during 2005.
In January 2005, Paramount Television announced that the series will enter rerun syndication in the fall of 2005, and that broadcasters covering 95% of the United States had purchased the rights to air past episode of the series (this is greater than the current coverage of UPN in the U.S.).
Spoilers
Some of the episode overviews may contain spoilers, but attempts are made to limit their spoilage.
T'Pol revives a previous job to seek a two-decade-on-the-run fugitive. During the mission, a dark secret from her past is revealed, shattering her emotional control.
After a short trip by Archer and Trip on a planet, Trip discovers he lost his communicator on the pre-industrial planet and is captured while trying to retrieve it.
The Enterprise encounters the Vissians, a more technologically advanced species, and Trip finds himself transfixed on the fact the Vissians are a three-sexed species.
The crew of the Enterprise first encounters the anomalies of The Expanse and learns of the existence of giant spheres that seem to be behind its existence.
During an unexpected wild goose chase pursuing the Xindi, Archer, T'Pol, and Hoshi are exposed to an alien virus and begin to mutate into members of a long-dead race called the Loque'eque .
A slave girl is accepted aboard Enterprise as a refuge, but spies on the crew instead. Meanwhile, Archer learns that synthesized Trellium-D can be used to protect the vessel from the anomalies.
The Enterprise encounters a Vulcan ship in which the crew has become "infected" by a potent neurotoxin related to Trellium-D that causes permanent neural damage. T'Pol becomes infected and loses control of her emotions, becoming paranoid and nearly homicidal.
An anomaly causes Archer to lose his short-term memory. Much of the episode takes place in an alternate future after the destruction of Earth in which Archer (with the help of his caretaker T'Pol and Captain Charles Tucker), seeks a way to correct the past.
Trip becomes comatose after a plasma manifold explodes and a clone of him is created. Archer's order to kill the clone in order to harvest a needed body part save Trip is met with resistence.
With the help of Daniels, Archer and T'Pol go back in time after discovering a group of Xindi reptilians are creating a biological weapon in 2004Detroit.
Enterprise encounters the Sphere Builders. T'Pol experences unexpected emotions and initiates a relationship with Tucker. Reed and Major Hayes come to terms with their differences.
After finding the weapon on Azati Prime, Archer embarks on a suicide mission to destroy it. T'Pol goes into an emotional tailspin as Enterprise suffers a devastating attack by the reptilian Xindi.
Enterprise is heavily damaged by Xindi and seeks exchange of Trellium-D for a warp coil from an alien vessel but is forced to steal it. T'Pol confesses her addiction to liquified Trellium-D.
Final showdown with the reptilian Xindi to stop the weapon from destroying Earth. Archer is lost and believed dead and Enterprise finds itself back in the Second World War era.
Season 4 (2004-2005)
Note: airdates and titles for yet-to-be-broadcast episodes are subject to change.
After destroying the Xindi weapon, the Enterprise finds itself in the 20th century during World War II with Nazis in the USA with high-ranking aliens in control.
Enterprise is welcomed home for saving Earth and the crew takes a much needed vacation while Trip & T'Pol visit Vulcan. Erika Hernandez becomes captain of the Columbia (NX-02).
Phlox continues to work on curing the lethal disease caused by Klingon/Augment hybrids while Trip lends a hand to the Enterprise to remove Klingon subroutines in the warp engine.
The final two episodes of the season are scheduled to air the same night.
Story arcs
Star Trek: Enterprise relied upon story arcs more often than previous Trek series.
The first two seasons had only two story arcs which reemerged sporadically, while the entire third season was a single arc that also included episodes from the second and fourth seasons. Beginning with the fourth season, the format of the series was altered so that the season featured a number of two- and three-episode arcs, which more than doubled the total number of arcs. A number of arcs overlap while some arcs set the scene for later arcs.
These episodes chronicle the tensions existing between Vulcan and Andoria, two worlds that eventually put aside their differences and ally with Earth to form the United Federation of Planets.
An unidentified force from the 29th century is attempting to disrupt history through a Temporal Cold War. These episodes involve a time traveller from the 30th century, Daniels, who works with Archer and his crew to make sure history is not changed.
A mysterious space probe attacks Earth, killing 7 million people. After receiving information from individuals involved in the Temporal Cold War as to the origin of the weapon, the Enterprise NX-01 is assigned to enter a dangerous region of space to track down those responsible and prevent further attacks on Earth. This arc spanned an entire season and also overlapped into both the second and fourth seasons. The fourth season in particular sees Archer and his crew dealing with the fallout from the Xindi mission, with references to the event occurring in more episodes than are listed below.
Genetically engineered humans created in the 20th century and nurtured by a brilliant but insane scientist hijack a Klingon vessel and attempt to rescue their adopted "father".
Vulcan undergoes an upheaval as followers of Surak's principles try to overthrow the current government which is being secretly manipulated by the Romulans.
The Romulans use the mental abilities of an Andorian race called The Aenar to control a series of prototype, remote-controlled vessels designed to spark a war between Earth, Vulcan, Andorians, and the Tellarites.
In this sequel to the human augments arc, the Klingons attempt to create their own genetically engineered race using Augment DNA from Dr. Soong's embryos. The result: a virus that is killing millions of Klingons and changing their appearance.
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Title
415
"Affliction "
416
"Divergence "
Birth of the Federation ("BOTF")
These episodes follow the early steps leading toward the creation of the United Federation of Planets. The arc incorporates elements of the Vulcan vs. Andorians arc, the Surak's follower's arc, and the Xindi arc.
