By Natalie Abrams
Updated October 27, 2015 at 01:26 AM EDT
Tina Rowden/FOX

Ichabod Crane, Abbie Mills, Temperance Brennan, and Seeley Booth walk into a bar. No, this isn’t the setup for a joke. Ahead of Halloween, the worlds of Sleepy Hollow and Bones will collide for a rare genre-bending crossover.

“What a stupid idea. I thought, ‘No way, different universes, it’ll never work,’ ” Tom Mison (Ichabod) recalls of his initial reaction to the pitch. And yet, here he sits on a late-September afternoon on the set of Bones, sipping a Sex on the Beach — which, according to Crane, Benjamin Franklin apparently once called a Fondle in the Forest — in the aptly titled Founding Father’s bar, his character toasting the unlikely foursome’s impossible achievement: finally getting along.

But let’s start at the beginning: The two-hour event kicks off in the more grounded universe of Bones, when a headless corpse lands in Brennan’s (Emily Deschanel) possession at the Jeffersonian lab, raising a red flag for Ichabod and Abbie (Nicole Beharie). “Immediately, we think it’s the Headless Horseman,” says Mison, which is why the Sleepy duo arrive to claim the body under the guise of an investigation. But it won’t be that easy.

After an awkward first meeting in which Ichabod is mistaken for a cosplayer, the quartet gravitate toward investigative pairings — as FBI agents, Booth (David Boreanaz) and Abbie are a natural fit, even though Abbie is on high alert. “We’re definitely hiding more of what our intentions are in their hour,” Beharie says. “For Abbie, that’s a little bit of a problem because she doesn’t want her cover blown. She wants to be able to still fight evil, but still have a career.”

That’s made especially difficult since Booth and Ichabod “don’t like each other instantly,” according to Mison. “[Booth] gets to throw in all of these subtle insults at Ichabod, who is trying to maintain his manners and respond in front of these two ladies. It makes for quite a nice dynamic.”

“You just look at him, what he’s wearing, these frocks,” Boreanaz says of Booth’s reaction to Ichabod. “Initially not only what he wears on the exterior, but how he talks, what he’s representing, he’s a big squint in a very historical mind.” For the record, Boreanaz insists Booth would win in a fight. “He’s just got a faster draw,” he says. But Mison counters, “Crane has been punched in the face by death.”

Ichabod and Brennan, however, are a different story. “They’re very, very similar,” Mison says. So similar, in fact, “they’re always trying to one-up each other intellectually. That makes for a good battle.”

“For Brennan and Crane, you have complete opposites in a lot of ways in terms of beliefs,” Deschanel says, noting that the show sets aside the Washington Irving short story on which Ichabod Crane is based, which is why those at the Jeffersonian don’t recognize his name — though they still suspect something amiss. “There’s a moment where Crane is nearly busted,” Mison says. “It’s one of those nice moments where he has to talk himself out of it… I quite like that the more Ichabod is here, the worse he gets at being a spy and covering his ass, but he manages to cover his ass.”

While the characters don’t get along, the actors themselves don’t feel the same way. “It’s great working with them,” Boreanaz says. “They’re a lot of fun. We get a chance to talk about how they deal with living and shooting in Atlanta versus living in Los Angeles.” Save for Sleepy Hollow scenes that don’t include Bones players, the entirety of the crossover was shot during a single week in Los Angeles, in part to accommodate Deschanel. “I asked not to fly, because it was just too soon after having a baby to go for work,” she says.

Tina Rowden/FOX

Viewers expecting the two shows to bend toward each other’s genres, however, may be sorely mistaken. The two parts are “very different tonally,” Mison says. “It’s really nice to see a transition from Bones into Sleepy Hollow and see the very few moments where they do interlink, where there’s weird dead bodies and mysteries — but they solve it with science, and we solve it with an old book and a founding father.”

“It’s fun to see those worlds collide,” Boreanaz says. “It’s like a Ghostbuster moment.” Though, with what the quartet goes through in the second, more fantastical hour, Deschanel likens it to another famous flick. “It’s like an Indiana Jones situation,” she says before realizing, “My character is essentially an archeologist, right, so same thing.”

After discovering the headless body actually belongs to the dangerous redcoat General Howe (Nicholas Guest) — who, unbeknownst to Team Bones, has been reanimated and raises a battalion of undead British soldiers — the crime fighters all find themselves in the bowels of the Capitol building, where they locate a secret door conveniently unlocked by the Mason ring on Ichabod’s hand. Brennan reacts in awe as the wall slides back. “We don’t have this on Bones,” Deschanel quips between takes on the set built especially for the crossover. “Walls don’t move like this.” But one question remains: Will the crossover make the ratings move, too? Boreanaz, for one, is hopeful. “We want to do a crossover with Empire, but they’re so large, we’d have to climb golden ladders to get to their sets now.”

The Bones-Sleepy Hollow crossover event airs Thursday at 8 p.m. ET on Fox.

To continue reading more on Bones and Sleepy Hollow, pick up the new issue of Entertainment Weekly, on newsstands Friday, or buy it here.