When insurance companies use it, they've got a great excuse. When writers use it, they're called lazy. But the deus ex machina, known in some circles as acts of God, can be a viable plot twist...especially when all other possibilities have been exhausted. Snub this literary technique if you will, but it's been used by some of the greats -- everybody from H.G. Wells to J.K. Rowling.
Here Comes the Calvary
We've all reached that point in a story, whether it's one we're reading or one we're telling, when it seems that all hope is lost. When the situation seems so dire, it's impossible to see any light at the end of the tunnel. When that happens, the writer has a few different options for untangling the mess.
The most controversial is arguably the deus ex machina. Loosely translating the Latin, this actually means "act of God." Through this technique, a heretofore unexpected event is suddenly thrust into the story from out of nowhere to solve or resolve a situation which was completely unresolvable only moments before. Picture this to get the general idea: A tense 60-minute chase has led us here, the Two Tails saloon. Hammerface McGee and his band of local rowdies is on one side of the bar, Sherriff Bullitt O'Neal is on the other with his trusty deputies and of course, Ramblin' Nell. It's a standoff, with everyone's gun pointed at everyone else. Nothing is moving in the room except the sweat on Hammerface's forehead. And somewhere, a clock is ticking away the tense seconds. There's only one way out of this: start shooting. And this is just what Bullitt is about to do...when suddenly, the bottles behind the bar begin to tremble. A glass totters along the top of the bar and falls to the ground. The entire room is shaking. Earthquake! Everyone dives for cover, and the standoff scatters.
This is an act of God, and many critics complain that it's a lazy writing technique. They argue that such interventions are unlikely. The officer who shows up to rescue the children in Lord of the Flies, the eagle that appears at the end of Lord of the Rings, the resolution of Jacob's feelings for Bella in the final Twilight book -- all are deus ex machina. Critics can call it lazy if they like, but this is one of the oldest plot devices known to writing. It originated with the Greek writers, who needed big moments with which to end their plays. The sudden and unexpected intervention was as good a choice as any, and still is. When used the right way, this plot device (like any other) can be quite satisfactory and believable (I can't fault it in Lord of the Flies). At other times, it's a bit silly (Stephen King wrote that the Hand of God detonated a nuclear warhead in The Stand, and this is not a joke).
But when something comes out of nowhere, it's bound to draw a certain amount of criticism. The beauty of writing a book is that you can always go back and change something. If you've written yourself into a tense situation, come up with a believable way out and link it to something that previously happened. If someone is going to suddenly appear and save the day, write a scene in which that character specifically references the place where he or she will later appear. Bury it if you like, make it hard to find and impossible to remember, but add it in.
Because there's nothing wrong with an old-fashioned dues ex machina every once in a while, but don't rely on it. Always be willing to explore many literary techniques and write in different ways. As you get better and better at creative writing, you won't need to rely on acts of God.