'Longlegs,' a Satanic horror movie starring Nicolas Cage, is being called one of the scariest films. Here's what happens in its blood-soaked ending.

• Osgood Perkins' new horror film, Longlegs, has received considerable buzz, largely due to its masterful marketing campaign.
• It stars Nicolas Cage as the titular devil-loving killer and Maika Monroe as the FBI agent on his tail.

"Longlegs" may or may not be the scariest movie of the decade, depending on who you ask, but it's certainly in the running to be the most talked-about one.

The satanic horror movie set in 1995 stars modern scream queen Maika Monroe (of "It Follows" fame) as Lee Harker, a preternaturally perceptive, introverted FBI agent thrust into a case that's stumped the bureau for decades.

Over 30 years, 10 different, seemingly unconnected families have been killed the same way: Fathers brutally murder their wives and children before killing themselves. The only commonalities are that each family has a daughter with a birthday on the 14th of any given month, and indecipherable coded letters signed by someone calling themselves Longlegs are left at each crime scene.

A team at the FBI, led by Agent Carter (Blair Underwood), has deduced that Longlegs, though not physically present for the murders, is the person somehow responsible for making the fathers kill. After Lee intuitively figures out what house another culprit is hiding in earlier in the film, she's brought on to help crack the Longlegs case.

The film has been building hype for months thanks to the studio Neon's terrific marketing. The campaign smartly gave away nary a plot detail and held back any glimpses of Nicolas Cage's spectacularly unhinged serial killer Longlegs. Now, it's finally in theaters, allowing eager horror fans into the world that writer-director Osgood Perkins crafted.

The tense, disconcerting film evokes a sense of dread for much of its runtime, creeping toward a twisty, blood-soaked ending that fills in most of the blanks but leaves a few other key questions unanswered.

Here's a complete breakdown of how the movie ends, including what Perkins and the cast have said about it in interviews with Business Insider.

Warning: Major spoilers ahead for "Longlegs," including a detailed description of the ending.

What happens in 'Longlegs?'

"Longlegs" is split into three parts. For the purposes of this explainer, I'm considering the entirety of Part Three (titled "Birthday Girls") the ending.

In Part One ("His Letters"), viewers are introduced to Lee (Monroe) and learn about the Longlegs killings as she's brought onto the case and begins investigating. We also meet Agent Carter's family, including his wife and young daughter, Ruby, who invites an awkward and obviously socially stunted Lee to her birthday party.

It quickly becomes clear that Lee and Longlegs have a twisted history between them, as Longlegs leaves her a birthday card, allowing her to cipher the other crime scene notes he left at the homes of the murdered families. However, the nature of their connection is kept a secret until the end.

Generally, you'd expect a movie about a serial killer to build a finale that involves a confrontation between the killer and the hero, but Perkins pulls a fast one. Instead, Longlegs (whose real name is revealed to be Dale Ferdinand Cobble) is captured a little over halfway through the film's runtime, which is the first time the audience sees his face.

It is, in a word, hideous. He's a strung-out-looking, aging glam rocker-type who's essentially deformed himself with bad plastic surgery, botox, and fillers, looking a bit like a melting candle.

Cobble is arrested in the middle of Part Two ("All Of Your Things") after Lee visits her creepy mom Ruth (Alicia Witt) at her childhood home and finds a Polaroid she took of Longlegs when he first visited Lee when she was a little girl, on January 13, 1974, the day before her ninth birthday.

Part Two also confirms what most watchers had probably already guessed: Lee was the little girl we saw in the movie's opening scene, being confronted by Longlegs when he drives up to her house in a station wagon.

In this part, Lee and Carter also go to the Camera family farm, where one of the murders happened in 1975. There, they find buried beneath floorboards a deteriorated, life-sized doll that looks like Carrie Ann Camera, the daughter who was the sole survivor of that attack.

Carrie Ann (played as an adult by Kiernan Shipka) has been housed at a psychiatric facility and catatonic in the 20 years since the murders, only emerging from her unresponsiveness when Longlegs visits her — right before Lee and Carter stop by. Speaking to Lee, Carrie Ann tells her that she'll do whatever "the man downstairs" tells her to do, including jump out the window. She also suggests she's seen Lee before, or someone who looks like her, at her house and that Lee has also forgotten something about her own past.

How does 'Longlegs' end?

Part Three is when all hell finally breaks loose. Longlegs (aka Cobble) is apprehended by the FBI. Agent Carter is satisfied and believes the arrest will allow the murdered families to have justice. But an increasingly uneasy Lee remains convinced that, as she theorized early on, Longlegs wasn't killing these families alone — he had an accomplice. When she goes in to interrogate Cobble herself, he speaks mostly in riddles and refuses to tell her directly who he is working with.

Finally, he cryptically tells Lee to "ask her mommy," gives a last "Hail Satan" for good measure, and then smashes his face open on the table in front of Lee, killing himself.

A furious Carter confronts a traumatized Lee, admonishing her for remaining convinced of her accomplice theory and informing her that Carrie Ann Camera killed herself earlier that day. Carrie Ann's death seems to suggest that Longlegs' algorithm of killings was completed, as only one day (that day, the 13th) was missing from the pattern — but that's a red herring.

Lee and another FBI agent, Agent Browning (Michelle Choi-Lee), go to her mother Ruth's house to bring Ruth in for questioning, given Cobble's comments before his death. When Lee goes into the house to find her mom, Ruth, dressed as a nun, kills Browning with a shotgun. When a stunned and horrified Lee goes to confront her mother, Ruth is standing with the gun aimed at a life-sized doll that looks exactly like Lee as a child.

Realizing her mother was working with Cobble, Lee tells her that she can stop and that Cobble is gone. Ruth replies, "You got him. Now he's free. And you're free too, baby girl." She shoots the Lee doll in the head, and black smoke emanates from the place where the doll's head once was — and simultaneously, from a disoriented Lee's head right before Lee passes out.

As Lee is unconscious, viewers get an explanation of what the hell has been going on, courtesy of Ruth monologuing over a montage sequence of past events.

According to Lee's mom, Longlegs, a devil-worshipping dollmaker, visited them when Lee was a girl in 1974. Her mother interrupted them, at which point Longlegs told her, in a sing-song voice, that if she let him in now, it would be "nice," but if she didn't, he'd come back as many times as he'd like.

Instead of allowing Lee to be taken by the devil, who is present in the dolls that Longlegs creates, Lee's mother makes a bargain with the killer: She'd help him do Satan's work, murdering other families by delivering dolls to them crafted to look like their daughters, dressed as a nun and under the guise of the doll being a gift from the church.

Satan would do his soul-corrupting work through the dolls to get the fathers to kill, and Lee's mom would simply have to be there to watch the deaths happen. Ruth says this deal allowed Lee to grow up, unlike those little girls in the other families.

When Lee awakens, she's alone in her mom's house. An eerie voice — possibly the devil himself — tells her she's "late for Ms. Ruby's birthday party." Realizing something terrible is about to happen, Lee rushes to Carter's house to find him, his wife, and Ruby there, with Ruth and the Ruby-like doll she's just delivered to them. It's clear that the family is under the devil's spell.

Carter tries to fight against the compulsion and fails, stabbing his wife to death in the kitchen. He emerges and goes to attack Ruby before Lee shoots and kills him to stop him. Lee's mom produces her own knife to finish the devil's work by killing Ruby, reiterating that she's doing this all for Lee — "just like I've always done" — and that she'll do it "again and again," despite Cobble's death.

Apparently realizing her mom is a full-on Satan worshipper now and a lost cause, a distraught Lee shoots Ruth in the head to save Ruby. She also attempts to shoot the Ruby doll, but the gun won't fire.

"You're real scum," Lee says to the doll. And then, the movie ends.

'Longlegs' leaves many unanswered questions

As much as is answered by Ruth's monologue in the final act (like who Longlegs' accomplice is, how and why the other families died, and what the deal is with those creepy dolls), there are still lingering questions.

For one, it's not clear why Longlegs or the devil initially targeted Lee. Her family situation is different from all the other targeted families. Most obviously, her dad doesn't appear to be present at all, and the dad is a key component of all the rest of the killings.

One theory might be that it has something to do with Lee's semi-psychic abilities — perhaps that made her attractive to the devil. But the film doesn't clarify that, and then again, there's no indication her preternatural intuition even existed at that point. Maybe it was her encounter with Longlegs and the devil that sparked it.

Also, during the interrogation scene right before he smashes his own face to a pulp, Longlegs remarks that Ruth was "the seventh she to be given the same choice — crimson or clover." This suggests that Ruth may not have been the first Satanic recruit brought on to the devil's mission in this manner. But again, there's no follow-up there.

One more pressing question relates more directly to the ending: What was up with that black smoke emanating from the Lee doll's head and adult Lee's head once the doll was destroyed?

BI asked Perkins — and he's not telling.

"I don't think I should say," the filmmaker said when asked what the black smoke was. "I think that that's for you guys to worry about. I mean, I know, but I'm not going to say."

Monroe, who plays Lee, confirmed that she believes the black smoke is "up to interpretation."

In a separate interview, Witt, who plays Ruth, gave her own idea of what she thinks the black smoke was.

"It's darkness. It's darkness that's in there, and then it gets released," Witt said.

This interpretation is also backed up by a line Longlegs says earlier in the movie, in a flashback, when he's making the Carrie Ann Camera doll.

"I know you're not afraid of a little bit of dark. You are the dark," he says as he puts a sheet over the doll's head.

This ending wasn't always Perkins' plan

Underwood, who plays Agent Carter, gives a quietly devastating performance in his final scene in the film. In it, Carter, under the control of the devil in the doll, visibly fights against the compulsion to kill his family. He told BI that he had no idea when he initially signed on to the movie that his character was a goner since Perkins hadn't finished the final scene when they spoke.

"Oz…said the script wasn't quite finished, but he had two or three ideas of where he was going to go with it," Underwood said.

Once he finally saw how his story would wrap up, Underwood was thrilled to have such a meaty moment.

"When he finished it, he sent me the scene and said, 'What do you think?' I was like, 'Dude, I love it. I love this, man. I get to play,'" he added.

Perkins explained that his intent when he starts out on a script is always to start with the end.

"There's always the intention to figure out the ending and then map yourself backward," he told BI. "It never really quite goes that way, and I always find myself careening toward, 'Oh, fuck. Here comes the climax, and here comes the crisis, and here comes the thing, and I hope it's enough.'"

"But in this case, it felt like the inevitable thing that was hiding in plain sight, right?" he added. "Anybody watching the movie, certainly a second time, is going to be like, 'Well, of course that's how that goes.'"

The big climax, Ruth's monologue, also got an overhaul. According to Perkins, they filmed a few scenes where Ruth said everything directly to Lee on camera, but they scrapped that plan when "it proved to be too long and too not-dynamic."

The ultimate scene that made it in — a montage of events with Ruth speaking over it — came in the editing room, where Perkins and the film's editor patched it together from existing footage.

In the end, the "stylized sort of bedtime story" way Ruth reveals the truth to Lee (and the audience) fits perfectly with what the movie is about, in Perkins' eyes: a mother telling a lie to their child.

Will there be a 'Longlegs' sequel?

Any horror fan knows that where there's a box-office hit, there's almost inevitably a sequel. For now, Perkins is satisfied leaving things exactly where he left them.

"The good news about making a movie is that you get to say it's over," he said when asked if he's thought about what happens to Lee and Ruby after the abrupt ending. "To me, a movie is a completed movement, and you get what you get. If you want to extrapolate forward, amazing."

That said, when asked directly whether there wouldn't be a sequel, given his feelings about endings, he hinted it was a possibility.

"Any sequel or any subsidiary project wouldn't be like starting at the end and going forward," Perkins said. "It would be something else: prequel or another movie in the universe of 'Longlegs,' or something very unexpected."

"Longlegs" is in theaters now.