The lamps shone o'er fair women and brave men;
Music arose with its voluptuous swell,
Soft eyes looked love to eyes which spake again,
And all went merry as a marriage bell;
~ Byron, Childe Harold's Pilgrimage, Canto III, v. XXI
Classic-movie enthusiasts probably know this: if there is a dinner, dance or party in a John Ford film, chances are one of two things will happen: (A) a serenade, or (B) an interruption, in the form of a battle, bad news, or an unexpected arrival. Wee Willie Winkie, The Searchers, Wagon Master, Drums Along the Mohawk: one interruption apiece. They Were Expendable: one serenade and one interruption. Fort Apache: one serenade and two interruptions (I think that might be the record). Rio Grande: two serenades and two incidents that feel like interruptions, even though they technically take place after the party's over and everyone's gone home. The Grapes of Wrath has an attempted interruption; How Green Was My Valley a couple of quasi-interruptions (an unexpected guest arriving at one party, an argument among the guests at another). If a punch thrown at a wedding reception counts as an interruption, The Quiet Man has one too.
At about this point, I started getting the feeling that somebody thought this was a good idea.
If you think about it a little more you'd probably realize this is a recurring device across films and stories in general; Ford films just seemed to refine it into a kind of art. For a famous non-Ford example, take the Twelve Oaks barbecue in Gone With the Wind, which ends with the men pouring out of the house to join the army at news of the Civil War's beginning. Or the serenity of Lady Ludlow's garden party in Cranford shattered by the news that THE RAILROAD IS COMING. Lord Byron captured the drama of the situation beautifully in that verse quoted above, and the verses that follow (do look them up sometime). B-Western scriptwriters caught onto it too: off the top of my head, I can think of at least twenty B-Westerns where a celebration of some kind is interrupted by a hold-up, bank robbery, cattle-rustling, horse-theft, fistfight, or some other knavery. B-Western screenwriting is plot scraped down to its barest framework, free of additional layers like character development, motivation or emotion. But you can still build excitement and humor off that framework, which is what the best examples of the genre do well. And the writers knew the value of an interrupted party.
So I started considering: what are the benefits to a story? I came up with a couple ideas of my own. First, a celebration of some kind gathers all or most of your story's cast together in one place. Whatever the interruption is, everyone is there to learn of it, react to it, maybe discuss it; you can choose anyone you like to take part in the reaction or discussion. If it's an important event, it's a catalyst for everybody.
Second—and I think this is more important—it creates a dramatic mood shift. It emphasizes the significance, and possibly the wrongness, of whatever is interrupting. It's a bit like what P.D. James observed in Talking About Detective Fiction (I am paraphrasing dramatically here), that one body in a country library automatically makes the crime more shocking than a dozen crimes in a big-city alleyway—because it's incongruous, it's out of place. Isn't it more of a shock to have a battle or bad news put an abrupt end to gaiety than to have it come when everyone is already sobered or on edge with expecting it?
I wonder in which medium it's easier to create the necessary atmosphere of gaiety, and then pull off that mood shift—fiction or film? What do you think? Have you ever written an interrupted party scene yourself, or can you name some other good examples from books or movies?