(written from a Production point of view)
Story arcs are story lines in Star Trek that are told over the course of multiple episodes. They are not simply two-parters or recurring characters and themes, but rather plots that are interwoven with other arcs and plot threads. An example of this is Star Trek: Deep Space Nine's introduction of the Dominion and the eventual Dominion War. Story arcs often take precedence over other plot elements and consume a series for several consecutive episodes, but in many cases (such as the Dominion War) they may take a back seat and re-enter the picture later on.
Prior to DS9, story arcs were a relatively minor part of the Star Trek universe. Star Trek: The Original Series and Star Trek: The Next Generation both largely restored the status quo ante at the end of each episode, and even two-part episodes were somewhat rare. This changed due to the stationary nature of space station Deep Space 9, which did not simply move on to the next adventure each week; characters' actions had lasting consequences, and the events of one episode directly influenced the next. At the time, Ira Steven Behr had to fight with Viacom over making the show so serialized. [1]
Star Trek: Voyager took the idea of the story arc in a different direction by setting itself aboard a starship as per the traditional Trek formula but stranding its crew in the distant Delta Quadrant. This both enhanced and reduced the prevalence of story arcs; while alien races such as the Kazon and Borg appeared in multiple episodes, the show was hampered by its very nature: the object was to leave familiar elements behind, which meant each plot thread had a limited life span.
Star Trek: Enterprise, like DS9 before it, often relied on story arcs such as the Temporal Cold War and the Xindi arc that took up the entire third season. By the show's fourth season, Enterprise wrapped up these story arcs and instead refocused on the show's prequel concept with a series of "mini arcs." Most season four episodes are two- or three-part story lines, with few stand-alone episodes.
Feature-length episodes
These episodes are originally broadcast in two hours, as opposed to the standard one hour. After their original run, feature length episodes are re-cut as two part episodes (see below), but are usually released in their original broadcast format as a single episode. They include:
- TNG:
- DS9:
- VOY:
- "Caretaker"
- "Dark Frontier"
- "Flesh and Blood"
- "Endgame"
- ENT:
Two-part episodes
These episodes air separately, but tell the same story. It is typical for the first part to end with the line "To Be Continued...". They are frequently used to end and begin seasons. Two-part episodes include:
- TOS:
- TNG:
- "The Best of Both Worlds" and "The Best of Both Worlds, Part II"
- "Redemption" and "Redemption II"
- "Unification I" and "Unification II"
- "Time's Arrow" and "Time's Arrow, Part II"
- "Chain of Command, Part I" and "Chain of Command, Part II"
- "Birthright, Part I" and "Birthright, Part II"
- "Descent" and "Descent, Part II"
- "Gambit, Part I" and "Gambit, Part II"
- DS9:
- "The Maquis, Part I" and "The Maquis, Part II"
- "The Search, Part I" and "The Search, Part II" (see below)
- "Past Tense, Part I" and "Past Tense, Part II"
- "Improbable Cause" and "The Die is Cast"
- "Homefront" and "Paradise Lost"
- "In Purgatory's Shadow" and "By Inferno's Light"
- "Favor the Bold" and "Sacrifice of Angels" (see below)
- "Image in the Sand" and "Shadows and Symbols" (see below)
- VOY:
- "Basics, Part I" and "Basics, Part II"
- "Future's End" and "Future's End, Part II"
- "Scorpion" and "Scorpion, Part II"
- "Year of Hell" and "Year of Hell, Part II"
- "The Killing Game" and "The Killing Game, Part II"
- "Equinox" and "Equinox, Part II"
- "Unimatrix Zero" and "Unimatrix Zero, Part II"
- "Workforce" and "Workforce, Part II"
- ENT:
- "Shockwave" and "Shockwave, Part II"
- "Storm Front" and "Storm Front, Part II"
- "Affliction" and "Divergence"
- "In a Mirror, Darkly" and "In a Mirror, Darkly, Part II"
- "Demons" and "Terra Prime"
- DIS:
- PIC:
Three-part episodes
Three consecutive episodes that air separately, but tell the same story.
- TNG:
- DS9:
- "The Homecoming", "The Circle", and "The Siege"
- "The Jem'Hadar", "The Search, Part I", and "The Search, Part II"
- "Tears of the Prophets", "Image in the Sand", and "Shadows and Symbols"
- VOY:
- "Scorpion", "Scorpion, Part II", and "The Gift"
- ENT:
- "Borderland", "Cold Station 12", and "The Augments"
- "The Forge", "Awakening", and "Kir'Shara"
- "Babel One", "United", and "The Aenar"
Multi-episode arcs
Multi-episode arcs tell a continuing story and are spread out through several different episodes throughout one or multiple seasons.
The Next Generation
- Q and the Enterprise
- "Encounter at Farpoint"
- "Hide and Q"
- "Q Who"
- "Deja Q"
- "Qpid"
- "True Q"
- "Tapestry"
- "All Good Things..."
- Worf vs. Duras
- "Sins of the Father"
- "Reunion"
- "The Mind's Eye"
- "Redemption"
- "Redemption II"
- DS9: "Past Prologue"
- "Firstborn"
- Star Trek Generations
- DS9: "The Sword of Kahless"
- Sela
Deep Space Nine
- Changeling infiltration
- Klingon War
- Eddington vs. Sisko
- Dominion Invasion
- The Final Chapter
Voyager
- Voyager vs. the Kazon
- "Caretaker"
- "State of Flux"
- "Maneuvers"
- "Alliances"
- "Meld"
- "Lifesigns"
- "Investigations"
- "Basics, Part I"
- "Basics, Part II"
- Q Civil War
- "Death Wish"
- "The Q and the Grey"
- "Q2"
- The Hirogen's Hunt
- Barclay and the Pathfinder Project
- "Pathfinder"
- "Life Line"
- "Inside Man"
- "Author, Author"
Enterprise
- Temporal Cold War
- Vulcan vs. Andoria
- Journey to Risa
- Archer's trial by the Klingons
- "Judgment"
- "Bounty"
- "The Expanse"
- Xindi War
- "The Expanse"
- "The Xindi"
- "Anomaly"
- "Extinction"
- "Rajiin"
- "Impulse"
- "Exile"
- "The Shipment"
- "Twilight"
- "North Star"
- "Similitude"
- "Carpenter Street"
- "Chosen Realm"
- "Proving Ground"
- "Stratagem"
- "Harbinger"
- "Doctor's Orders"
- "Hatchery"
- "Azati Prime"
- "Damage"
- "The Forgotten"
- "E²"
- "The Council"
- "Countdown"
- "Zero Hour"
- "Storm Front"
- "Storm Front, Part II"
- "Home"
Discovery
Picard
- Synth mystery
Subject arcs
Section 31
22nd century episodes
- ENT:
- "Affliction"
- "Divergence"
- "Demons"
- "Terra Prime"
23rd century episodes
- DIS:
24th century episodes
The mirror universe
The alternate reality
Q
Q-related episodes
- TNG:
- "Encounter at Farpoint"
- "Hide and Q"
- "Q Who"
- "Deja Q"
- "Qpid"
- "True Q"
- "Tapestry"
- "All Good Things..."
- DS9:
- "Q-Less"
- VOY:
- "Death Wish"
- "The Q and the Grey"
- "Q2"
- LD:
- "Veritas"
Non-consecutive arcs
Starting in...
The Original Series
- The Talosians
- TOS: "The Cage", "The Menagerie, Part I", "The Menagerie, Part II", and DIS: "If Memory Serves"
- Polywater intoxication
- TOS: "The Naked Time" and TNG: "The Naked Now"
- Shore Leave Planet
- TOS: "Shore Leave" and TAS: "Once Upon a Planet"
- Kor
- TOS: "Errand of Mercy", TAS: "The Time Trap", DS9: "Blood Oath", "The Sword of Kahless", and "Once More Unto the Breach"
- Khan Noonien Singh
- The USS Defiant
- TOS: "The Tholian Web", ENT: "In a Mirror, Darkly", "In a Mirror, Darkly, Part II", and DIS: "Despite Yourself" and "The Wolf Inside"
The Next Generation
- DaiMon Bok and his revenge attempts on Picard
- TNG: "The Battle" and "Bloodlines"
- The Traveler and his interactions with Wesley Crusher
- TNG: "Where No One Has Gone Before", "Remember Me", and "Journey's End"
- Picard as Dixon Hill
- TNG: "The Big Goodbye", "Manhunt", "Clues", and Star Trek: First Contact
- Lore
- TNG: "Datalore", "Brothers", "Descent", and "Descent, Part II"
- The Crystalline Entity
- TNG: "Datalore" and "Silicon Avatar"
- Alien neural parasites infiltrate Starfleet Command
- TNG: "Coming of Age" and "Conspiracy"
- Professor James Moriarty
- TNG: "Elementary, Dear Data" and "Ship in a Bottle"
- Arridor and Kol
- TNG: "The Price" and VOY: "False Profits"
- Vash and her relationship with Jean-Luc Picard and Q
- TNG: "Captain's Holiday" and "Qpid", and DS9: "Q-Less"
- Thomas Riker
- TNG: "Second Chances" and DS9: "Defiant"
- Riker and the Pegasus
- TNG: "The Pegasus" and ENT: "These Are the Voyages..."
- Borg and First Contact (the Borg's involvement with Earth's first contact in 2063 and the repercussions which followed)
- Star Trek: First Contact, ENT: "Regeneration", and TNG: "Q Who"
- Vulcan/Romulan Reunification
- TNG: "Unification I", "Unification II", "Face of the Enemy", and DIS: "Unification III"
Deep Space Nine
- Anti-alien sentiments on Bajor
- DS9: "Emissary", "Past Prologue", "In the Hands of the Prophets", "The Homecoming", "The Circle", and "The Siege"
- Bajor's entry into the Federation
- The Maquis' struggle for self-determination
- DS9: "The Maquis, Part I", "The Maquis, Part II", TNG: "Preemptive Strike", VOY: "Caretaker", and various DS9 episodes until "Blaze of Glory"
- The Dominion's threat to the Alpha and Beta Quadrants
- DS9: "The Jem'Hadar" through "What You Leave Behind"
- Kira and Odo
- DS9: "Heart of Stone", "Crossfire", "Children of Time", "Call to Arms", "His Way", "Chimera", and "What You Leave Behind"
- Kira and Dukat
- DS9: "The Maquis, Part II", "Civil Defense", "Indiscretion", "Return to Grace", "In Purgatory's Shadow", "A Time to Stand", "Sons and Daughters", "Wrongs Darker Than Death or Night", and "Covenant"
- Quark and Grilka
- O'Brien and Liam Bilby
- Dominion cold war
- DS9: "The Die is Cast", "The Adversary", DS9 Season 4 (esp. "The Way of the Warrior", "Homefront", and "Paradise Lost"), DS9: "Apocalypse Rising", "In Purgatory's Shadow", and "By Inferno's Light"
- Nog and AR-558
- DS9: "The Siege of AR-558" and "It's Only a Paper Moon"
Voyager
- The Hirogen and holographic technology
- VOY: "The Killing Game", "The Killing Game, Part II", and "Flesh and Blood"
- The Silver Blood
- VOY: "Demon" and "Course: Oblivion"
- The Q Continuum
- VOY: "Death Wish", "The Q and the Grey", and "Q2"
- Fair Haven
- VOY: "Fair Haven" and "Spirit Folk"
Enterprise
- Augments and Khan Noonien Singh
- Xenophobic Humans
- ENT: "Home", "Demons", and "Terra Prime"
Discovery
- Harry Mudd
- DIS: "Choose Your Pain", "Magic to Make the Sanest Man Go Mad", ST: "The Escape Artist", TOS: "Mudd's Women", "I, Mudd", and TAS: "Mudd's Passion"
Short Treks
- Rise of the Kelpiens
- ST: "The Brightest Star", DIS: "The Sound of Thunder", and "Such Sweet Sorrow, Part 2"
- Tribble troubles
Picard
- The Conclave of Eight attacks Mars (prologue flashbacks in chronological order)
- PIC: "Broken Pieces", "Absolute Candor", ST: "Children of Mars", PIC: "Maps and Legends", and "The End is the Beginning"