Sequel Episode

An episode in a series that serves as a sequel to a previous episode. Different from a Two Part Episode, in that there may be several episodes (if not several years) inbetween the first episode and the one that picks up the plot again.

To qualify, it's not enough to simply have an object, setting, or character from one episode appear in another, otherwise any series with a Rogues Gallery would consist almost entirely of Sequel Episodes. If Cop Show has the Main Characters arrest a thief and recover some stolen jewels in one episode, and a later episode has the thief break out of prison and cause some more havoc, that's just a One-Shot Character moving up to Recurring Character status. If, on the other hand, a later episode has the cops discover that the stolen jewels they recovered were actually fakes, and they have to interrogate the thief to find out where she hid the real jewels, that is a Sequel Episode; the plot resolved in an earlier episode is reopened and explored again in a new episode.

Obviously this only applies to series where Stand Alone Episodes occur somewhat regularly. If the whole show is one long Story Arc, there's not enough seperating the plot of one episode from another to make labelling it a "sequel" meaningful. However, if a series has multiple Story Arcs, it is possible for a later Story Arc to be a sequel to an earlier one.

Often uses Cross Referenced Titles. Related to Continuity Nod and Call Back.

Anime and Manga

 * Ghost in The Shell Stand Alone Complex actually categorizes its first-season episodes as "Stand Alone" episodes and "Complex" episodes, of which the former are Exactly What It Says On the Tin, and the latter are a handful of Sequel Episodes around one major Story Arc.
 * In Kirby: Right Back At Ya!, various episodes get this treatment, but special notability goes to "The School Scam" and "Teacher's Threat" (sequels to "eNeMeE Elementary"), which are actually titled "Demon Teacher 2" and "Demon Teacher 3" in Japan.

Literature

 * The Redwall series currently consists of several vaguely related stories that take place in the same universe. However, there are a few cases of Direct Sequels. Mattimeo was sequel to the Original book; Mossflower has a sequel in Legend of Luke and a prequel in Martin the Warrior, and The Bellmaker is a direct sequel to Mariel of Redwall.
 * Inverted in Agatha Christie's novels Murder On the Orient Express (published 1934), Murder in Mesopotamia (published 1936) and Death On the Nile (published 1937), all of which take place on the holiday that Poirot takes in the Near East. The inversion is due to the fact that the stories are prequels to each other, for in Poirot's chronology, he goes down the Nile, visits Mesopotamia, and then travels on the Orient Express, the events occurring in reverse publishing order.

Live Action TV

 * How I Met Your Mother: First there was "Slap Bet" where Marshall won the right to slap Barney in the face five times, as hard as he can, at any moment he chooses. Next season, we got the episode "Slapsgiving", where Marshall decides to dole out one of his slaps on Thanksgiving Day and spends the whole episode putting Barney through a Paranoia Gambit. Two more years pass, and finally "Slapsgiving 2: Revenge of the Slap" arrives: it's Thanksgiving again and Marshall decides to let Ted and Robin slap Barney in his place, and, once more, Barney spends the whole episode tortured by the knowledge of what's to come.
 * In the Buffy the Vampire Slayer episode "The Wish" the vengeance demon Anyanka creates an Alternate Universe where vampires rule Sunnydale. By the end of the episode The Verse is returned to normal and Anyanka is left powerless. Later that season, the episode "Dopplegangland" was driven by Anyanka's attempts to regain her powers, and maybe warp reality back into a vampire run hellhole while she's at it.
 * "Intervention" was one to "I Was Made To Love You".
 * I Carly: iThink They Kissed, where Carly finds out that Sam and Freddie shared a First Kiss is the Sequel Episode to iKiss where the First Kiss occurred.
 * The fifth-season Quantum Leap episode "Deliver Us From Evil" is a sequel to the second-season episode "Jimmy": Sam leaps into Jimmy LaMotta a second time, a couple years after his first leap, and finds that the happy future he should have caused is failing to occur (thanks to an Evil Counterpart whose goal is to Make Wrong What Once Went Right). This episode gets its own sequel later that season when the evil leaper returns in "Return of the Evil Leaper".
 * The X Files first season episode "Tooms" was a sequel to an episode earlier in the season, "Squeeze," one of the few they did like that. In the first ep they caught the Monster of the Week and in the later ep he was released from prison.
 * The episode "Irresistible" had the sequel "Orison", and "Pusher" had the sequel "Kitsunegari"
 * The episodes of Castle that deal with Beckett's mother's case feel like this.
 * In the Flash Live Action TV series the episodes "The Trickster" and "Trial of the Trickster" were several episodes apart but they were combined into one two-hour (minus commercials) "movie" for VHS release.
 * Bones's Gravedigger: first appearance in the 2nd season, caught in the fourth, put on trial in the fifth.
 * Doctor Who does this a lot. One notable example is The Curse Of Peladon and The Monster Of Peladon.
 * The Dalek episodes from "Army of Ghosts" to "Journey's End" directly follow on from one another. A similar use happens with Cybus Cyberman stories from "Rise of the Cybermen" to "The Next Doctor".
 * "The End of the World", "New Earth" and "Gridlock" are season-apart stories loosely connected to the Face of Boe's final message to the Doctor.
 * "Mission to the Unknown", the Dalek Cutaway, led into The Daleks' Master Plan, two serials later.
 * Satellite Five (and all the mess the Doctor's involvement caused) reappears in the series 1 finale, after an assumed one-off encounter with the Mighty Jagrafess in "The Long Game".
 * While Torchwood was a recurring Arc Words in series 2 (with the Doctor meeting a group identifying as the Torchwood Archive in "The Impossible Planet" and "The Satan Pit"), the Doctor's only direct encounters were at the founding in "Tooth and Claw" and his capture by Torchwood London in "Army of Ghosts".
 * Series 4, 5 and 6 have a recurring string of non-consecutive River Song episodes ("Silence in the Library"/"Forest of the Dead"; "The Time of Angels"/"Flesh and Stone", ""..., though from her point of view, they're prequel episodes.
 * The End of Time picks up from at the end of "Last of the Time Lords".
 * Psych had an episode called "Extradition: Canada" and another more recent one called "Extradition: Canada 2 (The Actual Extradition Part)".
 * Stargate SG-1 has what amounts to a Prequel episode: '2010' is set entirely in a Bad Future, with the future versions of SG-1 working to send back a warning. The episode ends when they succeed, then a season later in '2001' the events referenced as history in 2010 start happening and they have to decypher the Note to Self: to avert it.
 * Hercules: The Legendary Journeys has done this a number of times. For example, there was the episode 'King For A Day', where Iolaus has to impersonate a missing king. A season or two later came 'Long Live The King', where Iolaus has to impersonate the king again.
 * Star Trek features several of these, spanning multiple series. The TNG episode "The Naked Now," for instance, was a sequel to the TOS episode "The Naked Time."
 * Law and Order brought back its Not-O-J-Simpson character when "If I did it" was news. Keep in mind the character was from many seasons ago. Two other examples:
 * "Coma" featured comedian Larry Miller as a nightclub owner whose first wife died under mysterious circumstances. He was the prime suspect until a junkie came forward and confessed to the crime. The last scene of that episode was the cops viewing a videotape where the junkie was shown to have performed at the suspect's nightclub. Two years later (in an episode called "Encore"), Miller's character returns after his second wife is murdered. He looks like he's able to evade justice again, but this time.
 * The first season episode "Indifference", is based on the Joel Steinberg case. In that episode, not-Steinberg was convicted and sent to jail. Around the time the real Steinberg was released (a decade and a half later), the episode "Fixed" had the not-Steinberg character be released from jail, only to be gunned down and become the victim of the story.
 * Criminal Minds has Outfoxed, where the UNSUB is a copycat of a killer who first appeared in The Fox.
 * According to Jim has the season 6 episode The Grill II, which is a sequel to the season 4 episode The Grill.
 * Modern Family's second-season Valentines Day Episode, "Bixby's Back", is a sequel to the first season's "My Funky Valentine", at least as it applies to Claire and Phil.
 * Merlin has three Lancelot-centric episodes (though he appeared in a couple more) that encompass his Character Arc: Lancelot, Lancelot and Guinevere and Lancelot du Lac, making him the only character to have three episodes named after him.

Music

 * Iron Maiden had the tale of Charlotte the Harlot chronicled in 4 songs from 1980 to 1992: "Charlotte the Harlot" (Iron Maiden, 1980), "22 Acacia Avenue" (The Number of the Beast, 1982), "Hooks in You" (No Prayer For the Dying, 1990), and "From here to Eternity" (Fear of the Dark, 1992).
 * Metallica with "The Unforgiven" on their self-titled album in 1991, and then "The Unforgiven II" on the album Reload in 1997, and finally "The Unforgiven III" on the album Death Magnetic in 2008.
 * Megadeth had the fan favorite song "Hangar 18" on their 1990 album, Rust in Peace. In 2001, they released a sequel song, "Return to Hanger" on the album The World Needs a Hero.
 * Manowar had a unique case of prequel episode (song), with "Metal Warriors (Brothers of Metal Pt. 2)" released in 1992 on their Triumph of Steel album, and the "Brothers of Metal Pt. 1" released in 1996 on their Louder Than Hell album.
 * Overkill have: Overkill, Overkill II (The Nightmare Continues), Overkill III (Under The Influence), Overkill IV (E.Vil N.ever D.ies) and Overkill V (The Brand). Confusingly, they covered the Motorhead song Overkill as well (the source of the band's name, and a completely different song).

Web Comics

 * Sluggy Freelance gave us the horror movie spoof "KITTEN", and naturally it couldn't parody horror movies without parodying the inevitable sequels; hence, "KITTEN II".
 * Dragon City does this from time to time with story arcs. There was at least one story arc that have about four or five story arcs that were sequels of it and of each other since the latter ones were consequences of the first story arc.
 * Jix, which is by the same person who created Dragon City, also does this from time to time, but possibly not as extensively as Dragon City.

Western Animation

 * In Futurama the episode "The Cryogenic Woman" is essentially a sequel to the pilot episode (showing how far Fry's come, reminding us of what his life was like before he was frozen and showing how someone might suffer for being a Fish Out of Water in his situation). They even pointed this out in the DVD commentary.
 * During the episode "Parasites Lost", among the many changes to himself via a beneficial worm infestation in his body, Fry gains the ability to play a holophonor (it is said that not many people in the whole universe can play it, and the few that could can't play it well), cementing his relationship with Leela. However, to find out whether or not she loves the real him, Fry induces a Pygmalion Snapback by driving the worms out of his body. He tries playing the holophonor again, and as expected, he lost both his talent and his seduction over Leela. The episode ends with Fry practicing on the holophonor, but this is not revisited until "The Devil's Hands Are Idle Playthings", a Series Fauxnale centering on Fry's ability to play the holophonor.
 * For Adventure Time, there's Return to the Nightosphere/Daddy's Little Monster for It Came From the Nightosphere.
 * Crystals Have Power for Tree Trunks.
 * Hot to the Touch for Incendium.
 * for Too Young.
 * The Creeps for Mystery Train.
 * From Bad to Worse for Slumber Party Panic.
 * The 2nd season Kim Possible ep "Return to Wannaweep" is a sequel to the 1st season ep "Sink or Swim", in which Gill, a mutated former camper "buddy" of Ron's wreaks havoc. In the sequel ep, Wannaweep has been re-opened, and Gill has reutrned to his human form.
 * In the 4th season, the introduction of Hana, Ron's adoptive baby sister was a clear case of this. There are more than five episodes between Big brother and Oh no, Yono! but they are clearly meant to follow each other with plots-lines being started in Big brother coming to fruition in Oh no, Yono!.
 * The Angry Beavers, the episodes "Up All Night" and "Up All Night 2: Up All Day. The Reckoning". The first one concerns the beavers trying to stay up until morning, and eventually staying up until The Future. In the second one, they get back via a Deus Ex Machina and decide to go to sleep, eventually.
 * In the first episode of South Park (title "Cartman Gets an Anal Probe"), alien visitors probe Cartman. This wasn't brought up again (aside from a Clip Show Parody Episode) until the 100th episode, "Cancelled".
 * Recess: "The Big Prank" and "The Madness of King Bob"
 * The Powerpuff Girls had two instances: "Supper Villain" and "Just Deserts", as well as "Monkey See, Doggy Do" and "Monkey See, Doggy Two"
 * The Season 3 episode of Teen Titans "X" is essentially a sequel to Season 1 ep "Masks".
 * In The Simpsons, Homer and Ned get married to two floozies while drunk in Las Vegas. The episode ends with Homer and Ned leaving town and their second wives behind. In an episode a couple of seasons later, the two women reappear, having tracked them to Springfield.
 * Star Trek the Animated Series had several episodes that were sequels to episodes in Star Trek the Original Series.
 * "Mudd's Passion" to the episodes "Mudd's Women" and "I, Mudd"
 * "More Tribbles, More Troubles" to "The Trouble With Tribbles".
 * "Yesteryear" to "The City On The Edge Of Forever" (both involve time travel using the Guardian of Forever).
 * The Family Guy episode "Internal Affairs" is a continuation of "Foreign Affairs", as both go into Joe and Bonnie's deteriorating relationship.