Whether it’s the group of riders sweeping around the corner and charging into battle to save the day, or a powerful figure entering a boardroom to save the main character from corporate malfeasance, I think most people love a good last-minute intervention by the cavalry riding to the rescue. It’s a staple of entertainment.
I’m not sure about the psychology of it but if I had to guess, I would posit that it has something to do with elation accompanying the swing in emotions. When all seems lost and the protagonist (and reader) are nearing despair, there is a sudden ray of hope, a chance to escape—or even a chance to dish out some well-deserved retribution to the ones tormenting the hero.
But like any other staple, cavalry rescue as a plot device can lose its taste with overuse.
I read a book not long ago (I won’t name it out of respect for the author, who passed unexpectedly) that featured multiple uses of the trope. Too many. It got to the point that when the protagonists were in dire straits, I was waiting to see who was going to save them this time. And several of the instances made little logical sense, for the “cavalry” in question to be placed just-so, in order to effect a rescue.
I know, as a writer, it is very tempting to use the cavalry to resolve an issue. It’s dramatic, and we all love pumping up the excitement in a scene. On the other hand, if it’s done badly, it will come off as deus ex machina; in other words, the author made some shit up because they wrote themselves into a corner and didn’t know how to get out of it.
Deus ex machina is a more general problem for authors to avoid (such as a character randomly knowing magic or how to fly a starship when they didn’t before because the plot needs them to solve a problem) but I am going to stick to the dramatic intervention of outsiders for the moment.
So with these thoughts on the table, here are a few ideas to keep in mind:
1) Like all literary devices, use it sparingly. Like I said above, it got to the point in that book where I was looking for a rescue of the characters every time they got in trouble, and I wasn’t surprised by the third time, nor any after that. Not only does this remove agency from your protagonist—you’re telling the reader the main characters don’t drive the plot but are only players affected by everyone else—but it also removes or lowers the stakes. If your reader thinks your characters aren’t in any danger (whether they are or aren’t), they won’t be invested in anything that happens.
2) Time it properly. As noted, the properly-placed arrival of the cavalry can raise the dramatic stakes and multiply the excitement for the reader. Because it’s a multiplier, I think timing it toward the book’s climax, or at least at the end of a long significant sequence, will amplify the intensity already present. This isn’t a hard and fast rule but if you’re going with point one above, make the most of limited use.
3) Make it logical. I can’t stress this one enough. Yes, it might be cool for the hero of your medieval fantasy to be backed into a corner by orcs with no hope of escape, only to have a flight of modern fighters sweep overhead and bomb the attackers into oblivion … except there’s no plausible reason for fighters to be there and no way for your character to communicate with them. It doesn’t have to be that extreme. Even in said scenario, if the wizards who were thought to be on the other end of the world show up and attack, how did they get there? How did they know the hero was in trouble? This is something you can avoid with a little careful planning in advance, by creating earlier in the story feasible reasons for the cavalry to arrive.
I’ll use two examples from film/TV to illustrate what I’m saying. Lord of the Rings and Jurassic Park spoilers incoming.
In the second LOTR movie, The Two Towers, when Theoden leads his people to Helm’s Deep, Gandalf tells Aragorn to look to the east on the morning of the fifth day as he rides out to look for help. As the fortress is besieged and slowly overwhelmed, just as the defenders make a final suicidal charge, Gandalf appears leading a host of loyal riders who had been turned from Theoden’s service. The cavalry arrives in a nick of time, on the fifth day, just as Gandalf said they would.
To me, this was a good example of the cavalry saving the day (quite literally). It was timed perfectly and set up by the previous proactive actions of the characters. I’ll give a little allowance for Gandalf, being the literal incarnation of a minor god, to calling his arrival at just the right time.
In contrast, in the first Jurassic Park movie, the main characters are cornered and about to be eaten by a pair of velociraptors … before a Tyrannasaurus Rex bursts in and chomps one of the raptors, also distracting the other so the humans can escape. It’s timed well, coming at both the movie’s climax and the end of an increasingly-tense sequence.
Every previous appearance of the Rex had been accompanied by impact tremors—vibrations caused by something massive (like dinosaur feet) hitting the ground. Even if the humans hadn’t noted such tremors in their fear, the raptors, with their enhanced senses, would have, and would have reacted to the presence of a predator fifty times their body weight (this doesn’t even cover the raptors seeing Rex before it attacked, considering the whole thrust of the movie is that dinosaurs are related to birds, who generally see very well). And with an island full of prey that it can hunt, the Rex has little plausible reason to be present then and there, save for the plot demanding it. The characters didn’t do anything to bring it there, so it was pure chance. As much as I like the movie, it’s an illogical moment.
These are just examples and I am certain you can think of others, but I hope these have illustrated the point a little. For readers, it is fine to demand a certain level of logic from your plot and characters. Even in fantasy. For writers … look, just make it make sense.
That’s enough babbling from me. Cheers!