Impeded Messenger

A messenger has an important message/package/etc. for someone, probably the protagonist. Maybe they scheduled a meeting, making it a Doomed Appointment; maybe the protagonist doesn't know there is a messenger. One way or another, the messenger fails to deliver the message, or delivers the message too late. No relation to Unwitting Instigator of Doom, although an impeded messenger could become one.

As mentioned above, Doomed Appointment is a subtrope of this.

Film

 * Gallipoli has this as the major plot point in the film, where
 * The entire movie of Kangaroo Jack. Which is probably a good thing, as the money that the protagonists were supposed to deliver is meant to pay the recipient to kill them.

Literature

 * In the Discworld novel Thief of Time, it was mentioned that an Impeded Messenger example was averted when shortly after his horse threw a shoe, the messenger just 'happened' to run into a traveling peasant with a portable forge. This is played with further in that it is only due to the messenger's timely arrival that the dreadful Battle of Five Cities never happened.

Myths, Legends, and Oral Tradition

 * In the fairy tale The Armless Maiden, the Wicked Sister-in-Law changes letters to and from the titular character and her husband (who's away in a war), by getting the messenger drunk when he stops to rest at her place.

Theatre

 * Shakespeare:
 * The Impeded Messenger is a crucial plot point in Romeo and Juliet.
 * And a smaller point in Hamlet and in Tom Stoppard's Rosencrantz and Guildenstern Are Dead, where Hamlet changes the letter to the king of England so that R&G are executed in his place.

Video Games

 * Video game variant where the protagonist is the messenger: in Eternal Darkness: Sanity's Requiem, the character Anthony is given a scroll he's supposed to deliver to Charlemagne, but the scroll proves in fact to be a trap carrying a nasty undead curse—which Anthony discovers by accidentally inflicting it upon himself. Anthony bravely decides to warn Charlemagne of the plot against him, and after battling ghouls, traps, and the curse slowly eating away at his body, reaches his destination to find...that the assassins got sick of waiting, and Charlemagne is already dead.
 * Fallout: New Vegas starts with the player character as a Courier who gets ambushed by a group of thugs led by a man in a suit, who proceeds to take the Platinum Chip that was to be delivered. The main goal of the first half of the game becomes tracking down said man and regaining the chip (completing the delivery is optional after that though).