1. This trope is a mini story which occurs before the main plot. It is used to warm up the audience and set up the events which lead to the main story. Aside from being a catalyst, it usually has very little relevance to the rest of the episode. It may also be used to stretch the script to a sufficient length.
This trope differs from The Teaser in that:
- It does not occur before the credits (and is therefore not intended to grab the audience before a channel change).
- The Teaser does not have to be a separate set up, it can be an intrinsic part of the main plot.
A lead-in and a teaser are similar in that they both serve to bring the audience into the story.
- Often, an episode of Our Miss Brooks begins with Miss Brooks conversing with Mrs. Davis over breakfast. While the conversation usually has relevance to the plot of the episode, occasionally it'll just be a wacky interlude before the main story comes into play.
- Six Feet Under begins with one showing a person's death. The remainder of the show is sometimes related to that person, and sometimes not.
- MacGyver employed a variation on this in several episodes. An extended pre-credits sequence called the "Opening Gambit" was used several times, perhaps as a time-filler. It would be a short, self-contained adventure with an entirely different writer, production team, and supporting cast, and was often radically different in style from the rest of the episode (The titular character hardly ever employed any Bamboo Technology in the Opening Gambit), and featured its own credits. After the gambit, the titles would roll, and the story proper would begin. The only link between the gambit and the main story of the episode would be a voice over to the tune of "No sooner had I gotten back from that mission when they sent me on this one," designed to convey nothing more than that MacGyver leads a very action-packed life.
- Mystery Science Theater 3000's is usually its own self-contained comedy sketch, unrelated to the rest of the episode except for brief reference after the commercials.
- Sliders, mostly in early seasons, always started with the main characters in a random world ready to slide into the world that would be the setting for the episode. These lead-in stories rarely contribute to the main adventure itself (with some exceptions, like "The Breeder")
- Law & Order explores the activities of the people who discover the body in the minute or so before it is discovered.
- Many newspaper comic strips do this for Sunday installments. The first two panels will feature a small gag which is loosely related to the main one. This is done because the top row of a Sunday strip (which usually consists of two panels and the title) are often cut out by newspapers, so the main content of the strip can't begin before the second row of panels without alienating some readers.
- Family Guy uses this in almost every episode.
- The Simpsons have used a lead in with almost every episode. Sometimes, there's a Call-Back or Lampshade Hanging referencing the Lead In.
Abe: Aw, I can't believe we went through all that just to wind up with a tennis court.
- A Tale of Two Springfields [BABF20] — Badgers invade the family doghouse and Homer discovers that Springfield has been split into two area codes upon calling animal control. The split is the source of conflict for the rest of the plot. At the very end of the episode, we get a Call-Back with waves of long forgotten badgers invading Springfield. Lampshaded when, in the middle of a scene dealing with the area code split, the badger appears at the window, growling menacingly, before Homer tells it to "Go away, we got bigger problems now."
- Tennis the Menace [CABF07] — There's a notably long Lead In in which Homer helps Abe find a final resting place. During shopping around, the funeral director mentions that a very extravagant monument "will consume as much space as a regulation-size tennis court." The scene changes and Homer has used his money to build a tennis court rather than a tomb. Also lampshaded.
Homer: I'll bet you didn't see that coming.
- Simpson Safari [CABF13] — The episode begins with the Simpsons shopping at the supermarket. After a few gags, they reach the checkout lane, where we discover that the store's customers are making unreasonable requests to the bag boys, until they decide that enough is enough and go on strike. As a result of said strike, the Simpsons barely have any food left at home. They eventually discover Homer's old box of animal crackers, which has a prized golden giraffe inside. After negotiating with the production company behind the crackers, they go to Africa despite the contest being long over. There's a Call-Back later in the episode, where Homer begins to rant about the bag boys right before the family goes over an Inevitable Waterfall. Later on, they start following a chimp as Homer rants some more about the bag boys. Finally, at the end of the episode, there's a (rather harsh) dedication to bag boys.
- Ed, Edd n Eddy uses this every episode.
- SpongeBob SquarePants: "Biddy Sitting" opens with SpongeBob and Patrick starting a babysitting service, and Squidward doubting that they'll be successful. To prove him wrong, they babysit woman's many kids with unconventional, yet ultimately effective, methods. Nothing besides the babysitting service is brought up again: SpongeBob and Patrick don't spend the money they get, and neither Squidward, the woman, or her kids appear again. It mainly exists to set up the tone for the episode.
2. As in the expression "lead in audience".
A lot of TV viewers will watch a programme, then decide to watch the thing that is on next.
Therefore, having the right show before you can make a huge difference in your ratings- often over a million viewers (Lost in the UK shed 1.3 million viewers between premiere and its next showing; Big Brother wasn't on for the second week).
Stations compete to get good lead-ins for their local news broadcasts. At 5 or 6, it's usually a syndicated show, at 11 it's usually a network show. So, the NBC affiliate would often win the 11 o'clock ratings battle back when ER was on top at 10, and whoever gets Oprah will win at 5.
This is important, since all the local news broadcasts are more or less interchangeable in the mind of the viewer, and it's also usually the only ad revenue the station doesn't have to share with the network or syndicate. This was one of the reasons The Jay Leno Show, which was demonstrably hurting the 10/11 p.m. newscasts of NBC affiliates, was cancelled.
- Given that live eviction shows would be a highlights show and The Reveal, with a half-hour break before the exit interview, Big Brother, as mentioned above, was the example of this for Channel 4, supporting every series of The Friday Night Project and 8 Out of 10 Cats. Until the later series, where it began to need one of its own.
- Ever since it came back in 2005, BBC One has a habit of pairing up Doctor Who with its singing/dancing competitions. For the first two series, Strictly Dance Fever was used as a lead in, which was reversed for series 3-5 when 'Who' lead in to Any Dream Will Do, I'd Do Anything & Over the Rainbow. Then, during the Peter Capaldi years, the show was lead in by Strictly Come Dancing, often resulting in a later than usual time slot.
- Naturally, this was also the case with Robin Hood, which lead into Strictly Come Dancing for its first episode; The two shows were swapped for episode two and stayed that way for the first two series.
- M*A*S*H performed rather badly in the Ratings during its first season, when it was poorly placed in the CBS lineup. For the second season, CBS moved it between All in the Family and The Mary Tyler Moore Show, which instantly turned M*A*S*H into the hit we now know it as.
- Nickelodeon tends to show new episodes and/or marathons of SpongeBob SquarePants, The Loud House and PAW Patrol before new episodes of their other shows or before events on the channel like the KCAs.
- Cartoon Network does the same thing as Nickelodeon, but with Teen Titans Go!. They also occasionally did this with Adventure Time back when it was popular.
- The Muppets:
- Sam and Friends: During its heyday, the twice-daily series served the lead-in to the two highest-rated shows on WRC-TV, The Huntley-Brinkley Report and The Tonight Show with Steve Allen.
- The Muppet Show: While the show was made for First-Run Syndication, ITC Entertainment made a deal with CBS to air the show on their owned-and-operated stations, which aired it before the start of network's primetime lineup.
- The Simpsons usually starts their seasons in September (although, during the 2000s, they would start in early November due to Fox's contract with MLB to show the World Series in October). However, their season 10 premiere episode, "Lard Of The Dance", aired in August 1998 as the lead-in to the premiere of That '70s Show.