“Reunion time!” Jared Padalecki is making an announcement. It’s early December, and he and his Supernatural costar Jensen Ackles are preparing for their final two days of filming the 300th episode (Feb. 7) as demon-hunting brothers Sam and Dean Winchester, respectively. As they walk onto the Men of Letters set on a rainy Thursday, they come face-to-face with Jeffrey Dean Morgan, a personal friend and the man who brought Papa John Winchester to life in the show’s pilot (and left the show after season 2). “It’s the culmination of 300 episodes,” Padalecki says of Morgan’s return. After all, John’s disappearance kick-started the brothers’ road trip.

Image zoom Eric Ogden for EW

“Dad’s on a hunting trip, and he hasn’t been home in a few days.” Standing in his little brother’s college apartment, Dean Winchester first uttered those words in the pilot, and in doing so, launched Supernatural’s — and the brothers’ — first big mystery. “I had a good feeling about the show just reading the pilot,” Ackles says. “It had grit, the characters were well-written, and the story had miles to go.” Although he couldn’t quite predict how many miles the journey would be.

Supernatural premiered on The WB in 2005 and has since become the longest-running show in The CW’s history. The idea was simple: two brothers hunting monsters from urban legends, the kinds of things you’d hear about while sitting around a campfire. Bloody Mary? They killed her. Hook Man? Yep, him too. But it didn’t take long for the writers to understand that they might have to broaden the scope of the show if they wanted to get 20-plus episodes (much less 300). “We quickly realized that [conceit] would run out in a hurry, so even early on we expanded our horizons of what the show could be,” executive producer/co-showrunner Robert Singer says. But just how far could they stretch? And would they even get the chance?

Despite surviving the 2006 WB–UPN merger that created The CW, it took years for Supernatural to land on solid ground. “Bob Singer and I were fighting for the show’s survival at the ends of the first three seasons,” says creator Eric Kripke. “We’d have a meeting with the network that we informally called the ‘explain-why-we-should-give-you-another-season’ meeting.” And yet there was something about those conditions that felt right for a show about two humans trying to save the world from superhuman forces. As Dean recently said in a season 14 episode, “Impossible odds—feels like home.” But the land of impossible odds isn’t simply where the show (and the Winchesters) lived in those early years. It’s where they thrived. “In the beginning we almost mischievously wanted to see what we could get away with,” Kripke says. “There weren’t a lot of genre shows on The CW. It was mostly Gossip Girl and 90210. We were always like the goth kid at the back of the class that no one really wanted to pay attention to. So on this little weird horror show, we really got to push some boundaries that hadn’t been attempted in TV. There was no one saying, ‘That’s too crazy.’” So they took risks. They wrote a Groundhog Day-style episode called “Mystery Spot” that saw Dean die more than 100 times in one hour. They created “Hollywood Babylon,” an episode where Sam and Dean investigated a haunted horror-movie set. They produced “Ghostfacers,” an episode shot to look like a reality show about ghost hunting. “We always felt like we were on tenterhooks a little, but it helped us in a way,” Singer says. “We said, ‘If they don’t like us, let’s be bold.’ ” And in season 4, they made perhaps their biggest, boldest decision yet: They introduced angels (and therefore a much more religious story line) into the fold, which Singer identifies as the show’s biggest turning point. “I was concerned that would be a bridge too far,” Padalecki says of the angelic decision. “I wondered, ‘Are we going to turn o a lot of the people that came here to watch a scary movie?’” Kripke himself had fought the idea for years, until a pre–season 4 epiphany came to him while he was washing his face, of all things. “I realized the supernatural world was unbalanced,” Kripke says. “There was only evil. So I walked in the writers’ room on day one of season 4 and said, ‘Okay, there’s going to be angels…but they’re dicks!’”

Thus began what Kripke, who’s since created Revolution and co-created Timeless, still believes is one of the best hours of television he’s ever written: the season 4 premiere. “Lazarus Rising” introduced Castiel, the show’s first and longest-lasting angel. “Right before my scene, [then writer] Sera [Gamble] said, ‘Your life is about to change,’” remembers Misha Collins, who plays Castiel. He adds with a laugh, “I was like, ‘You’re so full of yourself.’” But Collins’ life did just that when he shifted from being a guest star to a series regular as his character survived multiple deaths — and even a brief stint as God — to become someone Sam and Dean consider family. “Angels completed the mythology,” Kripke says, and with them, the show was able to build to what writer-turned-showrunner Gamble refers to as the “regularly scheduled apocalypse” at the end of season 5. It was good versus evil. Michael versus Lucifer. Dean versus Sam. And for a while, everyone believed it was the end of the show. But when the network gave them a renewal for season 6, the writers were left to figure out what the heck comes after an apocalypse. The answer? Anything they wanted.

“A benefit of genre is we have such a huge runway in terms of ‘anything can happen,’” then writer and current co-showrunner Andrew Dabb says. “A medical show is limited in the scope of what they can do. We’re not.” So the next few seasons saw Supernatural push even more boundaries, with alternate realities, meta episodes (“The French Mistake,” anyone?), and new villains. That’s not to say everything worked, but that’s the beauty of a long-running show with a devoted audience — everything doesn’t have to work. “Fans would forgive sins of certain episodes because they love watching Sam and Dean,” Singer says. Because saying Supernatural fans like Supernatural is like saying Dean likes pie. It’s not about liking it. It’s about loving it. “I don’t think we have casual fans,” Singer says. “They live and breathe this show.” The #SPNFamily gathers all around the country (and globe) for multiple conventions each year, and every July they fill the largest venue, Hall H, at San Diego Comic-Con. It’s those fans who are devoted to Sam and Dean, even when their Impala might take a wrong turn. “The show’s ability to evolve and adapt is what’s led to it lasting 14 years,” Dabb says, adding, “Theoretically there are still a bunch of Leviathan out there running around that we never dealt with, but we don’t talk about that.”

Limitless options and viewer forgiveness aside, there is one rule the show has to follow — outside of standards and practices, that is. “I credit Bob Singer for instilling from very early on the idea that the show can go anywhere as long as the characters stay true to themselves,” former showrunner Jeremy Carver says. “The core of the show is the bond between the brothers.” With Sam and Dean as its foundation, the show can make episodes like season 11’s “Baby,” which was shot entirely from the perspective of the Impala, or season 13’s “Scoobynatural,” an animated crossover with Scooby-Doo and the gang. “One of the fun takeaways of watching Supernatural is that if you can imagine it, there’s probably a little town somewhere in America where it’s happening,” Gamble says. “It’s unlike any other show, really, in the history of American television.” And 14 seasons in, it’s still finding ways to surprise fans by, say, bringing John Winchester back.

Image zoom Eric Ogden for EW

“Dad?” Standing next to his little brother in the Men of Letters bunker, Dean can’t believe what he’s seeing. This time he’s not enlisting his brother to find Dad, because Dad has come to them. And he hasn’t changed much. His beard has more gray in it and his face is thinner, but it will surprise no one that John comes back with a rifle in his hand. (Sorry, Walking Dead fans; the rifle came before Lucille.) But John isn’t the only one who’s changed. Standing across from him, Sam and Dean are no longer the kids who crammed toy army men into the ashtray of the Impala, or even the young men who went looking for him in the pilot. They’ve grown up. Their lives, quite simply, have changed. The same can be said of the actors themselves. In fact, Ackles is currently two years older than Morgan was when he filmed the pilot. “That’s how full circle it all is,” Morgan says. “Like a father would be, I’m very proud of the guys. It makes me get choked up because they’ve done so well here. Episode 300? That’s unheard of.”

As for how John comes back, let’s just say things get weird — don’t they always? — and there’s an altered reality at play. “Our guys are put in a position where they essentially can have a wish granted,” Dabb says. “They’re actually expecting something else, but [John’s return] comes from a place of want by Dean. The need for closure is really what brings John back into their lives.” But John isn’t the only person who comes back into their lives. As with any altered reality, not everything changes for the good. Without getting too specific, whatever brings John back also causes the return of Zachariah (Kurt Fuller), the no-BS angel who saw Sam and Dean as nothing more than thorns in his side. (Like Kripke said, angels are dicks!) Speaking of angels, this reality also affects Castiel in… certain ways. This time the boys are dealing with a different (though not entirely unfamiliar) version of their friend.

Image zoom Eric Ogden for EW

But for Morgan, who’s been asked for years about returning, it has always been about bringing John back in the right way. “The relationships between these three men were so open, so if I was going to come back, it would be nice to have some closure, especially with Sammy,” Morgan says. And before the hour’s over, both boys will get a moment alone with Dad. “This episode gives Sam a chance to forgive,” Padalecki says. Ackles adds, “For Dean, the whole episode is a dream that he doesn’t want to wake up from. But he knows he has to.”

Back in the bunker’s kitchen where Padalecki declared “reunion time” just hours ago, Sam and Dean are sitting around a table sharing a bottle of whiskey with their father and catching him up on everything he’s missed. Yes, they’ve saved the world (more than once). Yes, Lucifer has a son. But most important, John’s late wife, Mary — the woman he spent his life trying to avenge — is alive. Right then Mary rounds the corner for the moment she never saw coming, but in a strange way has always been waiting for. “Everything’s right in the world in this bubble of time,” Samantha Smith, who plays Mary, says of the couple’s reunion. “It’s very romantic.”

But as the Winchesters know a bit too well, all good things must come to an end. And when this is said and done, Sam and Dean will return to their life, driving down crazy street next to each other. Because despite the show hitting 300 episodes, nobody’s ready to call it quits just yet. “I don’t think we’re ready to throw in the towel,” Ackles says. “We’ve still got a little gas in the tank.” Put another way, Sam and Dean still got work to do.