The folks at Wars and Politics of ASOIAF hold the wildfire under King’s Landing as a Chekhov’s Gun. As in, you don’t hang a gun on the wall unless you’re going to shoot it. In practical terms, the prediction is that since we’ve been made aware of a large amount of wildfire stored under King’s Landing for the past 20-or-so years, that wildfire is going to blow King’s Landing to tiny bits.
If I have to pick just one? The wildfire under King’s Landing. We know as readers that it’s there, from Tyrion’s and Jaime’s POVs. We also know – and this is equally important – that only two people in the world for sure know how extensive it is: Jaime and Brienne (though the upper-level Alchemists probably know as well). We know that wildfire gets more volatile as it sits (and this has been sitting for almost two decades). We know that the presence of dragons in the world makes wildfire more potent. We’ve seen how dangerous wildfire is, at the Blackwater – how it will burn through anything, and how it takes very little to set it off. And we know that, eventually, Daenerys will be coming to King’s Landing, with at least one dragon in tow. I have very little doubt in my mind Daenerys will, unintentionally, blow up the city of her ancestors.
Okay, that’s interesting, but I see a complication: the wildfire under King’s Landing is NOT so extensive anymore.
Granted, it’s been a while since I read ACoK, but I seem to recall Tyrion finding a whole lot of wildfire stored under the city, in some of the places Jaime mentioned later in telling Brienne about the wildfire plot. Tyrion had the alchemists use all that wildfire in the Blackwater battle. Tyrion didn’t know that he was finding evidence of the Mad King’s plot to destroy the city, and he didn’t know that his brother Jaime was already aware of the stuff being there, but either way, he found the stuff, and he had it brought up and poured into that ship that he used to set the Blackwater on fire.
Did he find all of it? Probably not. There may still be enough sitting around to do some serious damage if someone brings an unruly dragon to the city. I think Cersei poses the greater danger to the city, though. She’s the one who’s been repeatedly compared to King Aerys in the text; she’s the one who might actually try to destroy King’s Landing. Dany and her dragons might be a bull in a china shop, but I’m not feeling this scenario of Dany succeeding accidentally where her father tried and failed.
If I’m recalling Tyrion’s siege preparations correctly, then the Chekhov’s Gun was the story of the wildfire plot, which explained, in emotional terms, how Jaime became the Kingslayer, and in narrative terms, how Tyrion was able to defend the city the way he did. That gun’s already been fired.
Right, here’s an example, from Chapter 20, A Clash of Kings:
“Oh, but it does,” said Hallyne. “There is a vault below this one where we store the older pots. Those from King Aerys’s day. It was his fancy to have the jars made in the shapes of fruits. Very perilous fruits indeed, my lord Hand, and, hmmm, riper now than ever, if you take my meaning. We have sealed them with wax and pumped the lower vault full of water, but even so … by rights they ought to have been destroyed, but so many of our masters were murdered during the Sack of King’s Landing, the few acolytes who remained were unequal to the task. And much of the stock we made for Aerys was lost. Only last year, two hundred jars were discovered in a storeroom beneath the Great Sept of Baelor. No one could recall how they came there, but I’m sure I do not need to tell you that the High Septon was beside himself with terror. I myself saw that they were safely moved. I had a cart filled with sand, and sent our most able acolytes. We worked only by night, we—”
“—did a splendid job, I have no doubt.” Tyrion placed the jar he’d been holding back among its fellows. They covered the table, standing in orderly rows of four and marching away into the subterranean dimness. And there were other tables beyond, many other tables. “These, ah, fruits of the late King Aerys, can they still be used?”
“Oh, yes, most certainly … but carefully, my lord, ever so carefully. As it ages, the substance grows ever more, hmmmm, fickle, let us say. Any flame will set it afire. Any spark. Too much heat and jars will blaze up of their own accord. It is not wise to let them sit in sunlight, even for a short time. Once the fire begins within, the heat causes the substance to expand violently, and the jars shortly fly to pieces. If other jars should happen to be stored in the same vicinity, those go up as well, and so—”
“How many jars do you have at present?”
“This morning the Wisdom Munciter told me that we had seven thousand eight hundred and forty. That count includes four thousand jars from King Aerys’s day, to be sure.”
And from Chapter 49:
“No, no,” Hallyne squeaked, “the sums are accurate, I swear. We have been, hmmm, most fortunate, my lord Hand. Another cache of Lord Rossart’s was found, more than three hundred jars. Under the Dragonpit! Some whores have been using the ruins to entertain their patrons, and one of them fell through a patch of rotted floor into a cellar. When he felt the jars, he mistook them for wine. He was so drunk he broke the seal and drank some.”
“There was a prince who tried that once,” said Tyrion dryly. “I haven’t seen any dragons rising over the city, so it would seem it didn’t work this time either.” The Dragonpit atop the hill of Rhaenys had been abandoned for a century and a half. He supposed it was as good a place as any to store wildfire, and better than most, but it would have been nice if the late Lord Rossart had told someone.
So, over 4000 jars from King Aerys’s plot have already been found, moved and used. There’s not much ammo left in that gun.