I had the unfortunate distinction of probably having more experience with fiendfyre than any other teenager on the planet. Maybe more than most elderly dark wizards. I'd seen my godmother use it in very controlled circumstances when she taught me how to cast it. I'd burned my murderous mentor to death with it, along with our house. I'd narrowly escaped the last time Nott had used it to burn down the Shrieking Shack. I'd killed a vampire with it in the ruins of said shack. And now I was watching it unleashed on a mostly-sleeping collection of tens of thousands of people in flammable tents.
Since Nott had released the spell and then fled, it at least didn't have an intelligence, for all that it retained the image of a giant spider made of the purple fire. If he'd kept control, he could have directed it somewhat. Instead, it just moved like normal fire with a special effect. Well, like normal fire started with jet fuel that would ignore all practical attempts to put it out and burn faster toward the sources of magic it used as a power source.
Having a brainwave, Penny incanted, "Expecto Patronum!" and sent her birdlike patronus into the fire. Several of our other friends followed up with their own spectral silvery animals, either getting what she was going for or assuming she had a good reason. I couldn't fault her idea: the patronus was effectively the soulfire opposite of fiendfyre, and two of the other three soulfire charms were a counter for their hellfire analogue.
I wasn't sure it was going to work, and wanted to save my strength for my own idea. I yelled, "Fiendfyre! Everyone get back and move the people and the tents!"
To be fair, few people were stupid enough to stand around just watching an inferno, and most of the neighbors were already running. The braver ones took a moment to try to collect their things before fleeing. It was mostly just the Gryffindors and the veela still standing around, and the French witches might have some kind of natural resistance to fire. The werewolves had universally fled, probably spurred on by their inner wolves' fear of flames.
The set of patronuses smashed into the flaming spider and did, indeed, seem to slow its advance, if not extinguish it entirely. Bill lost two of his ushabti constructs before he managed to direct the rest to spread out, bodily slamming tents out of the way of the spreading fire and grabbing a couple bodies that had fallen in the fight at the treeline. The werewolf tents were a lost cause, but, drunkenly, Oliver had the presence of mind to incant, "Accio drinks trunk!" The werewolves' bar-in-expanded-luggage sailed away from the fire only slightly singed.
I was going to give him credit for stopping the flammable alcohol from exploding and not just trying to save the booze.
I'd already begun dragging my staff through the footpaths in a wide circle around the fire, hoping that I'd be able to complete it before the fire spread beyond its bounds. "Do you need 'elp?" Fleur yelled, over the roar of the fire.
"Do you know Waffling's suppression runes?" I asked, not stopping.
"Oui!"
"Start putting them along the outside of the circle! Spaced out about a foot should work," I ordered, then got back to what I was doing. I would periodically have to throw severing charms into the ground when it was too hard to make a significant dent with the end of my staff.
The rest of my friends were doing an adequate job containing the fire, between their patronuses and water-making and freezing charms. The problem was that fiendfyre could use magic as fuel, so conjurations were not nearly as effective as they would be on normal fire. Bill had worked out what I was doing, and had set Oliver and Charlie to scribing the other side of the circle while he added the runes.
"This is going to take a lot of power, Harry," he yelled across the fire.
"Do you know a countercurse for fiendfyre?" I asked. As a curse breaker, he might.
"Just being as strong as Dumbledore, and mentally overpowering the spell," he allowed, managing to multitask his rune-carving. Unfortunately, in addition to not liking the idea of running to the headmaster with all of my problems, he was an old man with an early bedtime hundreds of miles away. By the time a message got to him and he woke up and managed to make it here, the fire would be out of control.
Somehow, before the fire got loose, I met Oliver on the other side and completed the circle, though the ice barrier one of the veela had thrown up on our side was quickly starting to melt. I knelt down and finished the runes on my side as Fleur and Bill met me in the middle. I was able to check their handwriting and started incorporating it into my own mental model about how this impromptu ritual was going to work.
"Everyone stand back!" I ordered, before cutting my hand and letting some blood fall onto the circle. Nobody on the light side really loved blood magic, but when you absolutely needed a better connection to a ritual, it was the only way to fly. And I was pretty sure that just using my own blood and not casting on another person was legal, if frowned upon. Letting my thoughts expand to create the matrix of what I was trying to accomplish, I slammed my bleeding hand down just shy of the circle and yelled, "Finite Incantatem!"
I could feel the circle complete, at least, my magic latching onto the suppression runes and incorporating them into the general counterspell I'd just cast. It wiped out the conjurations first, and I worried I'd lost my eyebrows to the sudden blast of heat as the ice walls failed right in front of me. The spider shouldn't have any remaining intellect, but it seemed to chitter angrily and surge toward me, being forced back by my will.
Slowly, inexorably, the purple tinge left the fires burning in the circle and the giant violet spider danced toward the center. Face scorched and about to pass out, I gave one final push to my magic and watched the imago disintegrate back into flames. With no more animating magic, the fire inside the circle fell quickly to embers and a few patches of burning tent, no longer in much danger of spreading to the rest of the campsite.
I slumped over onto my side on the scorched grass and asked Oliver, only a few feet behind me, "You saved the drinks right? Because I need one."
It took a surprisingly long time for the aurors to show up. I'd had time to get that drink in a recovered camp chair while I sagged at the edge of magical exhaustion. Those that were good at healing charms and counter-curses were seeing to the injured. We'd been fortunate enough that no-one had died, but a few of the wolves, one of the veela, and a few of the bystanders had picked up more than token damage.
We also had three Death Eaters stunned, paralyzed, and bound that hadn't been able to escape with their peers. We were waiting for the authorities to unmask them, since apparently they had to be discovered actually wearing the masks for it to count.
"Well, well, Dresden. What will I be charging you with this time, do you think?" one of my least favorite voices in the universe asked. I tiredly glanced over to where Dawlish was standing with a couple of other aurors I didn't recognize. Strangely, rather than the rage-constipated look he usually gave me, he seemed kind of amused.
"Probably several counts of rescuing civilians and preventing mass murder while you all sat on your thumbs," I mouthed off. "Is making the auror department look bad a crime?"
"Maybe you missed the chaos everywhere else," he countered. "Rioting and muggle baiting near the stadium. This area was… less of a priority."
I rolled my eyes and snarked, "I'm sure the fiendfyre the Death Eaters left us would have stopped on its own before it got to the pureblood tents."
"You're claiming you stopped fiendfyre?" he asked, and I just gestured at the giant burned patch in front of me. The middle of it twinkled in the moonlight where it had been fused into glass. "Well that's a change, isn't it? You're usually the one starting it."
Again, the statement didn't have the bite it usually did, and I asked, "Going soft on me, Auror Dawlish? Or are you just not going to try to march me in with this many witnesses?" Indeed, the various conversations had fallen off as I'd been verbally sparring with the auror, and a bunch of people the purebloods would consider "dregs" were interested in his answer.
"The Ministry protects all its citizens and its guests," he finally allowed. "The other attack seemed to be a bunch of bewitched wizards and witches set loose to cover for the attack here, anyway." I guessed that would explain why the Death Eaters that came at us hadn't thrown a lot of really big spells: if they were all maintaining the imperius curse on someone else across the camp, it would have limited their power output. He ordered the other aurors, "Start taking statements."
"Might want to check the enemy combatants, first," I told him, pointing at the trussed-up captive Death Eaters.
He grudgingly did, and revealed two men I didn't recognize and one I did. "Marcus Flint!" Oliver yelled, gradually sobering up and also recognizing his former quidditch rival. The kid had been expelled from Hogwarts over a year prior for participating in the incident that had burned down the Shrieking Shack.
"Careful, don't hurt him," I said to Dawlish, sarcastically. "You might interrupt his plan to pretend that he was also under the imperius." Dawlish gave me a sour look, and I remembered, "Who was responsible for planning security for this thing anyway? It was you, right?"
Maybe the guy was stressed out that, indeed, Umbridge might not be able to protect him from this level of screw up, but he didn't give me the snarl I was expecting. He just shrugged and told his fellow officers, "Finish up here. I'll get these prisoners to the cells. You look rough Dresden. Don't overdo it."
As he portkeyed out, I wasn't sure whether or not I'd won that little exchange.