A/N: So, a little crossover to celebrate yesterday's releases of The House of Hades and SPN season 9. Minor spoilers for THoH, spoilers for SPN up through Purgatory.

While reading THoH, I noticed a lot of parallels between the Tartarus story arc and the Purgatory arc, e.g. main character and significant other (if you ship Destiel) are stranded in the place monsters go when they die. Basically a free-for-all where the monsters regenerate; theoretically there's no way out but there happens to be an escape hatch of sorts. Characters must fight their way out, facing old enemies, as half of the monsters in Purgatory/Tartarus are on their trail.

So, what would happen if Dean and Castiel and Percy and Annabeth actually were trapped in the same place? I see it the way they talk about the Underworld in PJATO - people see it how they want to - if they're Greek, they see it as the Underworld. If Egyptian, the Egyptian underworld. If Christian (or a hunter) they see it as Hell. And so on. Basically, Dean and Cas see themselves in a gray forest, Percy and Annabeth see themselves in a dark abyss with a river of fire and stuff. Since this story is from Dean's perspective, we see it as Purgatory.

Dean and Castiel have been in Purgatory for seven months and thirteen days when they hear of the other humans.

Benny mentions them in passing, in between battles. "It's just a rumor," he says. "Something the others have been talking about. You two aren't the only humans in here anymore."

"That's impossible," Dean replies. It's one of those rare calm moments in Purgatory, between battles, when they have a chance to stop and rest. "We got in by killing Dick Roman. How the hell would any other humans get here?"

Benny shrugs, focused more on cleaning his knife. "I only convey rumors. If you want, we could check it out. Only a couple of days' detour."

"We should go," says Castiel. "We should try to help them. Perhaps lead them with us to this escape hatch. If they're hunters, perhaps you know them. If not, even more reason to find them. Civilians in Purgatory will be dead within minutes."

Dean looks up at Castiel, holding his gaze for a few long seconds. "Okay, whatever you say. How do we find them?"

Benny nods to Castiel. "Same way we found your friend here. Kill until we find something that knows where they are."

It takes two days of searching to track down these mysterious other humans. They don't learn much more, only rumors. There are two of them, always together, a man and a woman. One of them is armed with a sword.

The sword bit makes Dean wonder if it's an angel, because in his experience only angels carry swords, but Castiel disagrees.

"I would know if one of my brothers or sisters was here," he assures Dean.

On the second day of fighting through Purgatory, the trio finally gets a location. They follow a trail of dead monsters to a loose clearing, ringed with trees. In the center are two vaguely human shapes, but Dean knows better by now than to trust that. Vampires and leviathan look human too, after all.

One of the strangers is sleeping, though. Dean's never seen a monster do that.

Dean stalks quietly through the trees, footsteps muffled. Benny, too, has perfected the art of silence. Unfortunately, Castiel has not. He steps on a loud branch, and the sound echoes through the empty trees. This time of day passes for night in Purgatory, when you can't see farther than ten feet in front of you and the skies are fogged a smoky black.

The guy jumps to his feet immediately, withdrawing something small from his pocket. A discrete knife, maybe.

"Annabeth," he says, tone edged with nerves and stress. This must be the girl, who jerks awake at the word.

Clearly they've been in Purgatory for some time, from the way Annabeth snaps immediately to her feet and into a fighting stance. Dean learned in the first hour that a fight could come from any side, at any moment.

"How many?" she asks, pressing her back against the guy's. They fight as a team, then, techniques in rhythm. They're comfortable with each other. Dean's chest twinges for a moment for Sam, and the comfortable familiarity of fighting at his brother's side.

The guy raises a sword Dean hadn't noticed before. And holy hell, this is a sword. It's not just a narrow knife, like Castiel's weapon, but long and double-edged. It's made of some kind of bronze, glowing faintly in the dark.

Dean leads them into the clearing, taking the first bold step. "Hey, relax, we're not here to fight you."

The girl raises her eyebrows. "Yeah, right. That'd be a first."

"I'm human, like you. You can trust me."

The guy looks like he takes Dean's words as truth, but Annabeth remains suspicious.

"Percy, stab him," she says.

Percy – that must be her friend's name – hesitates. "Annabeth, if he's telling the truth…"

"Then your blade won't hurt him."

Percy concedes to that and lunges forward.

Dean jumps out of the blade's reach just in time. "Whoa, hang on a second! Don't be so hasty. We just want to talk."

Castiel steps in front of Dean, protectively, possessively. Dean doesn't need a bodyguard, but he's flattered by Castiel's concern.

"How did you get here?" Annabeth asks. "Humans can't just waltz in."

"We were going to ask you the same thing," says Castiel.

"So, explain."

Dean lifts his hands in surrender. "We killed a monster and he dragged us along for the ride."

Percy laughs, actually laughs. It's been months since Dean's heard laughter. "That's exactly what happened to us." He lowers his sword. "I believe you. My name's Percy."

"Dean," says Dean. "This is Cas, and Benny."

"And you're what, a demigod?"

He shakes his head, temporarily thrown off by the question. "No, uh, just human. Cas here is… Well, anyway." He's still not sure he trusts them. He's still not sure they're human. "Benny is a vampire, it's true, but he's on our side. You can trust him."

Annabeth still looks skeptical. "We were just ambushed by vampires. I'm not a fan."

Percy steps forward, lifting his sword a little again. "Listen, I know it sounds crazy, but Annabeth has a point about the sword. Riptide is made of celestial bronze. If you really are human, it won't hurt you. Can I just…" He gestures with his free hand to Dean.

Dean doesn't understand most of what Percy just said, but he gets it. He has his own tests for demons and shifters. Whatever this bizarre test is, he'll go along with it. He shoves up the wrist of his jacket and bares his skin to Percy.

Percy drags his blade along the skin, but somehow it goes through Dean without leaving a mark. Wicked. He doesn't understand it, but Percy and Annabeth both seem satisfied by the result.

"Don't mind if I do few tests of my own, then," Dean says. "Cas?"

Castiel nods gravely. "They are both human, Dean."

That's good enough for him. He steps further into the clearing, and for the first time gets a good look at the humans.

Oh, God. They're just kids. They can't be more than twenty. Dean feels his heart plummet out from his chest. This situation – two kids alone in the woods, fighting monsters they can't beat – is all too familiar.

Percy turns, squinting into the darkness, sword half-raised in defense. "We should be safe for a few minutes. No monsters in sight."

Dean turns back to Benny, communicating with his eyes. Percy and Annabeth don't trust the vampire – for good reason – and they need someone to take watch anyway. Benny nods and takes up a position on the edge of the clearing, machete raised and ready.

Dean settles down beside the kids, keeping one hand curled around his knife grip. He remembers Benny's advice – trust no one.

"Listen, we know a way out," says Dean. "A backdoor out of this hellhole. Humans only. Come with us."

Percy and Annabeth exchange a look.

"We're headed for a different exit," Percy says. "We're meeting some friends at the doors."

Dean leans back, surprised. "You know about another? How long have you two been here?"

Annabeth shrugs a shoulder. "A few days. We lost count."

"A few- a few days?"

"Why, how long have you been here?"

"Something like seven months."

Percy's jaw drops. "How are you still alive?"

"We fight. We're fighting our way out of here. Surely you've experienced some of that."

"Only a little," Percy says, mouth quirking into a smile. Dean likes this kid. "Look, speaking of which… it's probably dangerous for you to stay near us for too long. We've got about half the monsters in Tartarus on our tail, apparently. And a few angry gods."

Dean laughs. Like that's anything new. "Listen, kid, you don't know the meaning of dangerous. Cas has pissed off every single Leviathan in Purgatory. Hell, I've probably killed half the fuglies down here, and I'm sure they're out for revenge. We're not exactly popular with this crowd either."

"Glad to know we're on the same page," says Annabeth. "We ran into some old acquaintances too. Those vampires I mentioned? I killed their ringleader a few years ago to save this idiot's life." She bumps Percy with a shoulder.

"So you're hunters, then." Seems basic enough. Somehow, these hunters got trapped in Purgatory too. Still, they seem too young to be hunting on their own, nonetheless batting in the major leagues.

Percy frowns. His eyes are a dusty green, ringed with fatigue and stress. "Hunters. Yeah, I guess that's one word for it. But if you're mortal, then how…"

"How am I still alive? Good question. Mostly thanks to that guy." He jerks a finger at Cas, who hovers just behind Dean, twitching at the slightest noise, poised for a fight. Always the protector. "He's an angel."

Percy smiles and sends a goofy, sentimental look Annabeth's way. "Yeah, I know what you mean."

Somehow, Dean isn't sure they're talking about the same kind of angel.

"Percy has a point," Annabeth says, "about the danger of this. If you're trouble and we're trouble, the two groups together could be…"

"Bad," finishes Percy. "Very bad."

Dean sees what they're implying, and he doesn't like it. "Are you sure you two don't want to come with us? We've got a way out," Dean repeats. He and his friends didn't spend two days searching just to be told "no thanks."

"So do we. Don't worry about us." Percy smiles wearily and wraps an arm around Annabeth's shoulders.

"Dude, you can't be more than eighteen, and you're trapped in God's asshole. I'm not going to abandon two teenagers to the Leviathan's wrath."

Percy shakes his head. "We can take care of ourselves. Don't worry, we've been doing this stuff for years and we haven't died yet."

"You think that's supposed to make me feel better? I've been doing this for thirty years and I've died five times, and Purgatory's still too much for me to handle most days."

Annabeth frowns, eyebrows creasing together. "That's impossible. Only immortals can-"

"Yeah, well, I keep getting lucky. Like I said, it's mostly thanks to Cas." He turns back to check on his friend. Cas stands absolutely still, the perfect soldier.

"We should keep moving," Percy sighs. He helps Annabeth to her feet, then extends a hand to Dean. "Thank you, for offering to help. We appreciate it, but we've got a job to do."

"I know the feeling. I'm still not pleased with this arrangement, though. On your own, you'll get killed in days."

Annabeth shakes her head. "No. Percy's got my back."

There's something very familiar about the certainty with which she speaks. Dean looks back at Castiel, gaze lingering for a moment. Castiel turns towards the conversation, curiosity in his eyes.

"Let's go," Dean tells him. "And you two... don't die."

"Yes sir," says Percy, mock-saluting him. "Good luck."

"Yeah, back at you," Dean says.

The two groups part ways, each to stop their own Apocalypses.