Spoiler alert: This story contains details from the season finale of HBO's "True Detective: Night Country."

The dark, twisted heart of HBO's "True Detective: Night Country" has centered on a chilling mystery – who (or what) killed the seven scientists found naked, frozen and grotesquely intertwined in a "corpsicle" outside their isolated research center in Ennis, Alaska.

All signs – including the recurring spiral, a callback to the anthology series' first season – pointed to something menacing and mystical.

However, in Sunday's Season 4 finale, police chief Liz Danvers (Jodie Foster) and state trooper Evangeline Navarro (Kali Reis) crack the case rocking the fictional Alaskan town and learn it was humans, and not supernatural forces, who were responsible for the murder.

Yet no one is arrested for the crime. Blame it on director, writer and executive producer Issa López's love of author Sir Conan Doyle.

"The Sherlock Holmes stories I love the most are (those) where Sherlock discovers the murderer, understands why the crime was committed, says he can't solve it and walks away," says López.

Here are answers to key questions in the finale:

Episode 5'True Detective: Night Country'reveals a stunning death. What happened and why?

Who killed the frozen naked scientists in 'True Detective'?

Yep, the cadre of male scientists weren't killed by mystical forces. Instead, the culprits are a band of vengeful women who work as Ennis' cleaners or in the crab processing plant. They are prompted after a simple mop bucket spill leads to the discovery of the station's nefarious secrets.

In short, it was the scientists who, six years prior, killed Annie K. They had panicked after Annie K had discovered their hidden lair of lies beneath the ice, and they stabbed the activist to death. Another "Night Country" mystery solved.

And the nail in the coffin for the scientists: They weren't just falsifying pollution numbers from the mine. They were pushing the mine to produce more pollutants, which softened the permafrost and made their delicate job of extracting DNA from frozen microorganisms significantly easier. The scientists were conducting potentially world-saving research, but pushing the mine to make the town toxic to devastating effect.

López says the actors playing the avenging "Night Country" women proudly dubbed their characters "The Justice Ladies."

The Justice Ladies are shown in flashbacks busting into the science station to take matters into their own hands. The panicked scientists are forced to undress at gunpoint and run naked into the brutal Arctic storm. Voila, corpsicle!

"These women are invisible, which is a tremendous disadvantage socially because justice is never going to be served to them," says López. "But at the same time, it's their superpower. They have access and can do things that nobody will suspect them of doing. That includes a big murder."

Raymond Clark (Owen McDonnell), the one scientist who escaped their killing wrath, confesses to the evil scheme to Navarro in an iPhone video. Clark then kills himself by running into the Arctic storm for one last, gloriously gruesome corpsicle.

So it's case closed.

Danvers and Navarro don't arrest the Justice Ladies, even after hearing a substantial confession. Danvers hides the truth about the spate of Ennis deaths (the scientists, and that of crooked Hank Prior in last week's episode) from investigators. "Some questions don't have answers," she shrugs.

Does Navarro die at the end of 'True Detective'?

It's not a happy "Night Country" ending, but a quietly triumphant one as the polluting mine is shut down once the Clark confession video goes instantly viral.

Danvers is shown laughing with her once estranged stepdaughter, a relationship on the mend. "This is not to say they're happy forever, but it's a beginning," says López.

After being kicked out of the house, officer Peter Prior (Finn Bennett) reunites with his family. But Peter's face becomes troubled holding his son; he was no doubt thinking of being forced to kill his father. Those thoughts aren't possible to erase like the blood he wiped up.

"He will carry that forever," says López. "But as Danvers says in Episode 6, 'It's crazy what we survive.'"

Navarro's fate is unclear. Finally at peace with so many parts of her life, including her fear of what's on the "other side" of life, Navarro is shown walking out onto the Alaskan ice, a serene look on her face.

"It could be Navarro goes on a walkabout, like they do in Australia, and then comes back in peace," says López. "Or she walks out in peace, not in torment, to join the women she knows on the other side."

Danvers visits Navarro's starkly empty house, and the investigators ask where Navarro is. So she went missing. In the final scene, Navarro is standing, staring into the distance on Danvers' sun-strewn Alaskan summer porch. Has she returned? Or is it her spirit returning to visit the living Danvers, as spirits do in "Night Country."

"It's really up to you to decide," says López.

As Danvers says to investigators, "This is Ennis; nobody really leaves."