Warning: Major spoilers ahead

Liz and Evangeline head to the ice caves, where Evangeline squeezes through a small gap – having had a premonition that it’s “this way”. The pair make their way through the tight cave but come to a dead end. Evangeline is adamant they’re in the correct place, but suddenly she falls through the ice to a cavern below. Just as she’s about to go get help, Liz falls through the ice too, and now they’re both stuck.

Unsure of what to do, Clark suddenly appears behind them and the pair follow after him, discovering an underground lab. They find a hidden exit behind some shelves and make their way up the ladder and through a hatch which opens straight into the Tsalal Research Station.

When Liz and Evangeline split up to try and find Clark, Liz finds herself getting locked in the freezer by him. He then heads into the corridor and hits Evangeline over the head with a fire extinguisher. Having broken out of the freezer, Liz finds Evangeline beating him up.

Back at Liz’s house, Peter gets to work cleaning up the crime scene and hiding any evidence. Leah arrives at the house ready to spend New Year’s with Liz and is surprised to find Peter there cleaning, but he uses the situation with Kayla as an excuse as to why he’s acting strangely. The pair leave so he can drop her back to Kayla’s.

Liz and Evangeline tie Clark to a chair so they can interrogate him. Evangeline puts headphones in Clark’s ears and puts the video of Annie’s last moments on a loop so he has to listen to it over and over. After sufficient time has passed, they remove the headphones and ask Clark if “he was there”. He says Annie started to piece together what they were doing, revealing the microorganism they were digging for did work – with the pollution from the mine helping to soften the permafrost, which meant they could extract the DNA with much less damage.

The scientists encouraged the mine to release more pollutants – as it created a better environment for their work – despite knowing that the polluted water was causing deaths amongst the local community.

Asking what happened to Annie, Clark shares that she had destroyed all the lab’s work after finding out what was going on, and that he ran downstairs after hearing her screams to find Lund attacking her. When she began to fight back, the other scientists “finished the job”. Clark denies having any involvement in her murder, but a flashback shows him suffocating her to death. When Evangeline questions why they cut out her tongue, Clark reveals that it wasn't them.

Later on, they ask him what happened with the scientists, to which he responds “she killed them”. Clark shares he kept seeing her and hearing her voice, knowing she’d eventually come for them. His flashbacks show him hiding beneath the station and holding the hatch shut whilst his fellow scientists’ screams can be heard in the distance. Clark claims that Annie has been hiding in the caves for years – long before she was born – leaving Liz to walk out in frustration.

Liz wakes to find the research station without power and a dead Clark frozen in the ice. Evangeline let him out, knowing that he would kill himself. With the backup generator not working, the pair are left freezing and without light.

Rose gets a visit from Peter, who repeats the line that Evangeline told him to say: “Take me to where Julia is”. Liz asks a shaking Evangeline what she’s doing to which she responds: “There is something out there calling me”. Evangeline brings up Holden, which angers Liz as she doesn’t want to talk about her dead child. Once she calms down, Liz returns to find an unresponsive Evangeline walking out towards the water in the thick of a snowstorm. Liz begins to hear her son calling out for her and spots him trapped below the ice, so she hits at the ice and falls through straight into the freezing cold water before Evangeline – having come out of her own vision – pulls her out.

Rose and Peter break through the ice and dispose of the bodies. Evangeline and Liz – having waited out the storm – toast to the New Year, but something Evangeline says about holding the hatch sparks a thought for Liz. Rushing into the room where the hatch is, she pours chemicals over the outside of the hatch, before shining a UV light – revealing a handprint. This leads Liz to realise they’ve been asking the wrong question – they should have asked “Who knows who killed Annie?”.

They drive over to speak with Beatrice and Blair – cleaners from the research station. They confess to finding the underground lab at the research station and that their community went there, armed with weapons, forcing the scientists out on the ice. They forced them to take their clothes off and left them there “for her to take them”.

Evangeline and Liz leave, agreeing it’s just a story, and that the forensic investigation concluded the scientists died from a slab avalanche. As she’s leaving, Evangeline asks about Annie’s tongue but Beatrice denies having any knowledge.

Later on, we see Liz being interviewed by police about the disappearance of Hank Prior and Otis Heiss. She delivers the pre-agreed story before being asked what happened with Evangeline, who left Alaska after everything happened.

But she did leave behind a video confession from Clark, where he revealed all the details about the pollution from the mine – a video which was later leaked and subsequently led to the mine being closed down.

Liz denies ever leaking the video or having knowledge of where Evangeline is, but we see the pair together at Evangeline’s new home out on the water.

In the final episode, we see Liz emerging from the research station to find Clark frozen into the ice with Evangeline watching over him. Liz suggests she let him out knowing that he would kill himself.

In an interview with Entertainment Weekly, showrunner, writer and director Issa Lopez confirmed the theory, and said: “That’s exactly what happened. I mean, he's given them everything he can give them because what he told them is his absolute truth. That's all he has. And he's asking to die, for her to let him die. And so she's going to give him that.

“Part of her is like, f**k you, no, because she doesn't want to give this murderer anything. But another part of her thinks he deserves to die with whatever is outside, number one. And number two, she needs the video and he's willing to give it to her.”

In the final episode, we finally find out the answers to some of the questions we’ve had all season, including who murdered Annie K. In a shock twist, it turns out that the Tsalal scientists are the ones who killed Annie after she realised their role in hiding the real pollution figures from the mine.

As for her tongue, this seems to be the great mystery even Detective Evangaline Navarro couldn’t quite figure out. Early on in the series, we find out that the tongue found at the Tsalal Research Station belongs to Annie K – a victim from an unsolved case years prior.

In episode five, we discover that Hank Prior, a fellow police officer, was tasked with moving Annie’s body – suggesting that he was the one that removed her tongue.

But who placed it at the research station? This remains an unknown with Issa Lopez, in an interview with Entertainment Weekly, suggesting a couple of potential options but confirming neither.

She said: “Is it perfectly possible that when the body was found by the community, someone kept her tongue as a gesture of reverence and respect and knowing that there was going to be an opportunity to come back? Maybe that happened, and they preserved that tongue because Danvers in episode two says there was some cellular damage, and it was weird. It could be because of freezing or not, we don't know.

“So anyways, the tongue disappears. Or it could be that the tongue is kept in a different place waiting for Annie to come back and leave it there as a sign that this is now finally when she gets to tell her story through the women.”

This is another thread that is open to interpretation. At the end of the final episode, we see Evangeline and Liz basking in the sunshine on a porch overlooking a lake – but whether that was real or a vision we don’t know.

Lopez refused to confirm either way, telling EW that it was “up to the interpretation of the audience”.