Doomed Appointment

One person promises to meet someone else (usually the protagonist) somewhere at a specific time, there to give them some information or object. Of course, this nearly guarantees that the messenger will be unable to make the meeting. A standard way to prevent the meeting is to simply kill off the messenger before the meeting is to take place, although abduction is another option.

Sometimes the person who was supposed to be at the Doomed Appointment was going to give the hero information that the writers don't want the viewer to have until later in the series, but they want the viewer to know that the information is out there.

The character who sets up the appointment may be a Turncoat of whatever group is opposing the protagonist(s), in which case that group will probably be responsible for preventing the meeting.

Disconnected by Death is a subtrope of this.

Pretty much the opposite of the Almost-Dead Guy.

Anime and Manga

 * The Soldats member from Noir who was going to give Kirika and Mireille a copy of the book regarding Noir that they were looking for.
 * A teacher at Narumi Ayumu's school in Spiral who intended to give Ayumu information on the Blade Children after school ended.
 * In a specially angsty version of this trope, Jim in Outlaw Star asks a girl out, neither knowing that each of them pilot opposing spaceships. Jim destroys the enemy vessel, but doesn't find out the reason she never showed up for their date is because he killed her.
 * In Death Note has a meeting with the police to tell them about her deductions in the case of Kira. All of which would point to Light Yagami would the taskforce know about them. However, as this happens in volume 2 of 12 she is killed by Light before she can talk to the police.
 * Considering the more or less Contrived Coincidence of her meeting with Light, the official book states her luck as lower than abysmal.
 * Kimi ga Nozomu Eien; As a matter of fact,
 * In Monster, Eva's life has gotten progressively more miserable since her father's death, but after ten years' worth of becoming a bitter shell she finally starts to find some measure of happiness again in a relationship with her divorced gardener. The gardener invites her to meet his daughter, but his wife comes back just a few minutes before Eva arrives. This finally proves to be the breaking point for her sanity, and she burns her house to the ground along with the garden.
 * And then the series decides to do it to her again, this time with Martin, a bodyguard that ends up developing a thing for her. When the organization employing him decides that Eva has outlived her usefulness and orders him to kill her, he instead arranges for her escape and promises to meet her at the train station at a specified time..
 * During the Chuunin Exam arc of Naruto the examiner, Hayate, overhears Baki, the representative from Sand Village--with whom Leaf Village was supposed to be allied--talking to a Sound Village spy about their plans to attack Leaf Village. He rushes off to tell the village leader, but Baki intercepts and kills him before he can do so. In doing so, he single-handedly created Naruto's biggest Ensemble Darkhorse while simultaneously making himself The Scrappy. Good one, Baka.
 * in the Soul Eater manga, who is killed on his way to an appointment with Marie after
 * Specifically, he noticed the presence of the insanity consuming the city, and then one of Death City's . Though in the chapter itself, the nature of his death was not clear.
 * Hughes from Fullmetal Alchemist. Though technically the information he had to relay and the appointment he was due for (His daughter's birthday) were two entirely separate things, but it still counts.

Comic Books

 * A familiar setup for Tintin stories.

Film

 * In The Net, Sandra Bullock's character is to meet a male friend at the airport; he is flying a small plane by himself, coming to discuss a secret file in person, when his navigational equipment is tampered with, and he crashes into a factory smokestack. This, as stated above, would have let loose far too much information, for the scriptwriters liking.
 * For some reason, the Devil lets the priest warn Robert Thorn in The Omen about his Antichrist son before killing him, even though the entire setup to that point is textbook Doomed Appointment.
 * In the second Pirates of the Caribbean movie, Governer Swann tries to meet with a friend of his who is a captain. Just as he arrives, his friend is killed by the villain's right hand man.
 * In another Johnny Depp movie, Blow, the "protagonist" (for lack of a better word) wants to pull One Last Job before running away with his daughter. He is betrayed by former colleagues, who are working for law enforcement, and is unable to meet his daughter at the appointed time. The film attempts to make the audience sympathetic to the main character, who is one of the top cocaine smugglers, potentially responsible for many deaths and destroyed lives.
 * The villain in Space Mutiny (Mystery Science Theater 3000) tosses the would-be Turncoat off of a high catwalk. The reason he was up there in the first place... ???
 * He was calling to check on his gender!
 * Happens to in Hot Fuzz. Amusingly while he is still killed seconds before he can deliver his message, he was killed for entirely unrelated reasons.
 * Especially ironic, due to the fact that his information  wouldn't have helped anyway, because it was wrong.

Literature

 * Happens twice in John le Carré's novel Smiley's People, although considering the high stakes involved  it's very much justified.
 * In the city watch books of the Discworld series this happens alot with Comander Vimes, although he usually tries to make it happen (e.g. someone dies but instead of sending another person, he goes and ends up missing appointments.)
 * The "Canary" Murder Case: When Tony Skeel fails to show up, Philo says he's probably already dead.

Live Action TV

 * In the last episode of season 3 of Angel, our eponymous vampire is supposed to meet Cordelia to discuss their relationship. It would be spoilery to say how, but neither of them make the appointment.
 * Setting up a meeting with Steed and Mrs. Peel to tell them some bit of vital information was a surefire way to die in The Avengers.
 * In the Buffy the Vampire Slayer episode "Passion," Jenny is working on the spell to restore Angel's soul and tells Giles she wants to see him later, but doesn't tell him what she's working on. Naturally, Angel kills her moments after she completes her work. Therefore we know the spell exists, but Buffy and the Scoobies don't.
 * Occurs in the pilot episode of Monk. It's dramatic but ultimately pointless, as Adrian Monk knew the messenger kept the information written on a scrap of paper in his hat.
 * The first episode of Women's Murder Club begins with the protagonist standing by her car waiting impatiently for a reporter who's supposed to meet her there. The reporter actually does soon show up... crashing into the roof of the protagonist's car, her corpse having been thrown from a nearby roof.
 * In Dollhouse, one of Echo's "clients" wants to relive the moment he showed his wife what he had accomplished... but in his fantasy, his wife doesn't miss the appointment due to a fatal car accident.
 * In a recent CSI Miami, a suspect's lawyer, walking through a park, called Caine about information she would only relay in person, as soon as she could get to him. The very next second, a mysterious man slit her throat while she was still on the phone with Caine. It may have set the record for quickest time from Doomed Appointment to doom.

Video Games

 * An entire level of the video game Jedi Knight: Jedi Academy revolves around a Doomed Appointment.
 * The death of in Resident Evil 4. Though his does live long enough after the fact to hand over
 * In the World of Warcraft Deathknight starting area, you get the quest to intercept a messenger (dooming his appointment), kill him, take his information and clothing and later pose as him. Actually, now that I think about it, you do that quite a lot in this game...
 * Kicks off the plot of Max Payne.
 * Ditto for the first level of Oni.

Visual Novels

 * In Shikkoku no Sharnoth intended to meet with  to confess her lover after a conversation she had that made her finally pluck up the nerve, but he never showed up