Many shows have some form of structure to their seasons, rather than just being collections of stories. This article mostly assumes that the series in question are US full-length series of around 20-26 episodes with some to low Season Fluidity. Even in cases of British Brevity, the season opening and closing episodes will tend to be similar in style to those in the US, regardless of the season's length.
This will often be big and spectacular, to lure viewers back to the show. It is not uncommon for new characters to be introduced to the show or for major plot changes to take place. See also Premiere and Pilot. It is also one of the most likely places to find a double length episode (and even when the first two episodes are both normal length, it's not at all uncommon for networks to show them back to back).
Lucky Episode 13:
Some series only have the first 13 episodes of the first season commissioned, with the promise of more if it is successful. For this reason, the writers will work out a 13-episode arc plot so that if the series is not renewed, it will still have a satisfying ending. If it is renewed then they need only rewrite the final script or so to introduce another threat or more plot threads.
The Ep-15 Shift:
Episodes 15-16 of a season tend to fall around the time of (February) Sweeps, so networks will have big spectacular episodes to attract viewers. Plot shifts are not uncommon here, as these are the early installments of the "Back 9" extension.
Season Finale (Ep-20 to Ep-26):
Again, big and spectacular, usually tying up all of that season's emotional and plot arcs, although an end-of-season Cliffhanger is possible. There may well be character departures by various different means. In cases where the season finale is made prior to the decision on whether or not to renew the show being made, expect a finale that ties off most major plot threads, but leaves enough dangling to make it easy to carry on if the show is renewed.
If this is a two-season drama —even if the seasons are of irregular length— prepare to be burned.
Expect abundant use of Series Fauxnale (an installment that served as a Grand Finale prior to getting uncanceled) in the mid-season game-changers. Related to Story Arc (the sequences told in a story). Super-Trope of Front 13, Back 9 (the lucky 13th episode). Compare Strictly Formula, when the main plotline of every episode is basically the same; this trope is similar but on a season-wide scale.
Anime & Manga
- My-HiME: The Searrs arc ends in episode 15 (in a Your Princess Is in Another Castle! moment), and episode 16 introduces a new and unexpected plot twist.
- The Return to Gravity Falls: Going under the 10-episodes-per-season layout, the first episode introduces the mystery of the set, the 5/6th has big secrets pertaining to the mystery, and episodes 9/10 (or maybe even before nine) is the end of the arc.
- 24: The nuclear explosion in season two is an example of the episode-15 shift.
- Alias: "Phase One" is a textbook example of a mid-season shift.
- Babylon 5: Although it's the ninth episode instead of the fifteenth, "The Coming of Shadows" elevates the classical mid-season shift to the point that it won a Hugo Award.
- Buffy the Vampire Slayer:
- "The Freshman" opens the fourth season with Buffy and the gang starting college; which is a game changer in terms of setting and, to a lesser extent, of cast.
- As per the formula, the 15th episodes have a tendency to pull a mid-season shift of major proportions.
- In the second season, the two-parter "Surprise" & "Innocence", Angel's soul is destroyed after sharing a tender moment with Buffy.
- In the fifth season, Buffy's ill mother, Joyce, suddenly collapses in "I Was Made To Love You". The following episode, "The Body" confirms that she died from a brain aneurysm.
- Castle: Each of its three full seasonsnote has a major two-parter with a big guest star representing a federal agency right about this time. They were:
- Season 2's "Tick, Tick, Tick..." & "Boom!", guest starring Dana Delaney, playing a specialist from the FBI.
- Season 3's "Setup" & "Countdown", guest starring Adrian Pasdar, playing a member of the Department of Homeland Security.
- Season 4's "Pandora" & "Linchpin", guest starring Jennifer Beals, playing a member of the CIA & Soviet operative.
- CSI: Miami: Horatio Caine's trip to Brazil in "Rio" opens the 5th season with a game-changing blast.
- Doctor Who: The two-parter "Bad Wolf"/"The Parting of the Ways" ends with the regeneration of the Ninth Doctor into the Tenth Doctor and Captain Jack Harkness being left behind on the space station for reasons the Doctor wouldn't explain until the Series 3 finale.
- House: "Broken" opens the sixth season with House's stay in the mental hospital. It mentions that he will be seeing his doctor for outpatient therapy after being discharged. This is not referenced again until a couple of episodes before the finale.
- The House of Eliott: A three-season Period Drama with ten episodes per series and no finite plot, more similar to an American series than the typical British literary adaptation or original period miniseries, ended on a cliffhanger with one of the sisters threatening to walk out on the eponymous fashion house. However, The BBC then decided not to commission another series, so the series was left dangling.
- Our Miss Brooks: The controversial fourth season began with the aptly named "Transition Show", in which Madison High School is torn down for a freeway, and Miss Brooks and Mr. Conklin find new work at Miss Nester's Private School.
- "In My Time of Dying" opens the second season with pretty much everything going wrong. Sam and Dean's father dies to save Dean's life and the Colt, which can be used to avenge their mother, disappears with him. This prompts Sam and Dean to gather what clues they have to finish what their father had been working on for over twenty years.
- The 16th episode of any season is usually pretty dramatic, and often a season game-changer.
- Season 1's "Shadow" has Meg being revealed as a villain and the brothers finally reuniting with John, albeit briefly.
- Season 3's "No Rest for the Wicked" was the season finale due to the writers strike, and includes Dean being dragged into hell.
- Season 4's "On the Head of a Pin" has the first big sign that Castiel is good, the revelation that Dean broke the first seal, and the revelation that Uriel is actively trying to help Lucifer rise; he is then killed.
- Season 5's "Dark Side of the Moon" has Dean and Sam in Heaven, and the revelation that Castiel's plan to search for God really is fruitless.
- Season 6's "...And Then There Were None" kills off no less than three recurring hunter characters.
- Terriers: Its season finale is a textbook example that works as either a cliffhanger for the next season or a satisfying resolution to the series. (It turned out to be the latter when the show was not renewed.)