A mysterious note from a stranger changes the plot in some way. Generally, it is shoved under or into something such as a locker, postbox, or a door. If the recipient sees the note drop on his mat and dives for the door, he will occasionally catch the messenger in the act of posting the note; however, the messenger usually leaves so fast it's as if he teleported.

Can be anything at all, for example:
* A clue from an anonymous source
* A note from a past or future self
* A revealing tape of some kind
* A threat of some kind
* Ransom demand
* Invitation
* etc

Not to be confused with BrownNote or any other sound related trope, although it can contain, or be a recording of any kind.
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!!Examples:

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[[folder: Anime & Manga ]]

* In ''Manga/OresamaTeacher'', both Mafuyu and Hayasaka receive notes in their lockers saying "360 degree warning". This presages the appearance of a new character, a wacky fake 'ninja' who is trying to destroy the Public Morals Club.

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[[folder: Fanfiction ]]
* In ''Fanfic/HarryPotterAndTheMethodsOfRationality'', one of the results of Harry's experiments with a [[FantasticTimeManagement Time Turner]] is a note from his future self reading only "DO NOT MESS WITH TIME"
* The Fanfic/AllGuardsmenParty's [[AllegedCar discount spaceship]], the ''Occurrence Border'', is covered with little yellow post-it notes bearing helpful messages such as [[GravityScrew "The gravity in this corridor is tilted 37 degrees to the left"]] or, all too often, [[DontTouchItYouIdiot "Do not ever touch this button."]] That's in realspace, though, once the ship lurches its way into [[HyperspaceIsAScaryPlace the Warp]], more notes start showing up in areas the party has already visited, with always helpful but disturbingly specific advice like "In case of {{bad dreams}} check [[FantasticRadiationShielding Gellar Field]] [[OhCrap integrity."]]

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[[folder: Films -- Animated ]]

* ''WesternAnimation/TheIncredibles''. The "note" is in the form of a digital tablet with a video message inviting Mr. Incredible to do secret superhero work.

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[[folder: Films -- Live-Action ]]

* ''Film/MurderByDeath''. While Sam Diamond and Miss Skeffington are in their room, they hear a ticking sound. A note is slipped under their door that says, "That ticking sound is a bomb that will go off in 30 seconds. Signed, The Murderer."
* In ''Film/{{Unsane}}'', a horror/thriller author receives one about a series of murders related to his latest book.
* ''Film/{{Memento}}'': The hero receives a few of these. Some of them from himself, since he suffers from anterograde amnesia.

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[[folder: Literature ]]

* ''Literature/{{Home}}'': Frank Money receives a note that says, "Come fast. She be dead if you tarry." This causes Frank to start his journey home to save his sister.
* In ''Literature/TheHoundOfTheBaskervilles'', Sir Henry Baskerville receives a message consisting of words cut and pasted from the ''London Times'' warning him to stay away from the moor (where Baskerville Manor was).
* Mysterious poison-pen letters (together with pranks and outright vandalism) are part of a plot against Shrewsbury College, Oxford in ''[[Literature/LordPeterWimsey Gaudy Night]]''.
* A couple of these appear in ''[[Literature/AuntDimity Aunt Dimity Takes a Holiday]]''. The notes' author employs the classic pasted-letters-cut-from-printed-material technique.
* In ''Literature/TheGirlFromTheMiraclesDistrict'', [[spoiler:Ture]] leaves Nikita a note serving as a SequelHook, promising her that "the truth" is hidden in a remote Norwegian village.

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[[folder: Live Action TV ]]

* In ''Series/TheXFiles'', Agent Mulder repeatedly receives revealing documents on various conspiracies from his informants. They try to be sneaky about it.
* In an episode of ''Series/MagicCity'', an envelope is shoved under the door. When opened, it contains a photo with "$20,000" written on the back. The photo shows one of the heroes in bed with a mobster's wife and is clearly an attempt at blackmail.
* Mysterious notes or objects are often the catalyst for Scott Wolter's investigations on ''Series/AmericaUnearthed''.

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[[folder: Pinball ]]

* In ''[[Pinball/WHODunnit WHO dunnit]]'', HardboiledDetective Nick Spade receives an unsigned note asking him to meet someone in the basement of Tony's Palace. It's actually a setup for an ambush by the murderer.

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[[folder: Video Games ]]

* ''VideoGame/SilentHill4'': Henry can receive messages from the dark world if he slides blank pieces of paper under his door. [[ShameIfSomethingHappened Better go check on your neighbor!]]
* VideoGame/TheDreamMachine has it's main plot started by one Viktor finds in his new apartment.
* ''VideoGame/{{World of Warcraft}}'': At the start of the Mists of Pandaria legendary questline, you receive this [[http://www.wowhead.com/item=87261/mysterious-note conveniently named item]], indicating that the last of the Black Dragons wishes to recruit you to save the world.
* You can get these from couriers in ''VideoGame/TheElderScrollsVSkyrim''. The most common and benign are letters from "a friend" who heard you [[MakeMeWannaShout Shouting]] somewhere and give you directions to another Word of power you can use as you develop your Dragonborn skills. More ominous is an annonymous note you receive if you start looking into the [[MurderInc Dark Brotherhood]], which consists of nothing but an image of a black hand and the words "WE KNOW." [[spoiler:The next time you sleep after getting this note, you'll be kidnapped by one of the assassins, who makes a macabre recruitment offer.]]

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[[folder: Webcomics ]]

* In ''Webcomics/AutumnBay'', IntrepidReporter Felicia Kingsley receives one from "a friend" when she is supposed to meet a contact. It is pinned to a post and has her name on it.

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