In Bir Tawil, a lawless territory in the middle of the desert, Rachel, Maggie and a new group of scientists test bacteria from their research on humans for the next phase of the trial. But after an uninvited visitor and an unexpected death, Maggie and Rachel fear their worst nightmare is happening all over again.

As Maggie begins to recount details of how the members of the team were killed, the search team discovers a frozen hand peeking out from the snow near the base.

In the middle of the winter, a small group of scientists in charge of an international base in the Antartica during the long polar nights stops communicating with the outside world.

The summer team tries to find clues of what could have happened during the winter, unveiling a first possible suspect.

Arthur reveals that the body found by the team was that of Sarah Jackson's. Meanwhile, Maggie discloses that Sarah's death was not an accident. She was murdered.

Winter has fallen on the South Pole. A small team, known as the Winterers, will remain at the Polaris VI Antarctic Research Station to continue their innovative research, a crucial part in the fight against climate change. After the winter, Johan Berg returns to base, finding most of the team dead or missing. Only Maggie remained at the station.

Jolted by the revelation of Sarah's death, Maggie reveals that the killer was looking for something which Maggie found and kept with her.

As the Alexandria threatens to explode, the remaining scientists jump ship and onto the only life boat – putting them face-to-face with the real killer.

After breaking out of his confinement, Charlie cuts the ship’s power once again and embarks on a murderous rampage. As Olivia finds herself one step closer to Rachel, Gloria pulls away from Wilde.

With Charlie locked up, Amy brings lingering doubts to Wilde, confirming his greatest fears. In the U.K., Olivia and her sister are attacked while plotting their revenge.

After a forceful shift in power, both scientists and subjects do whatever it takes to stay alive -- even if it means turning on one another. Following a jarring discovery, the remaining subjects attempt to escape the facility, while, at Portlaoise, Arthur receives an unexpected visitor.

Far from land, Arthur Wilde and his team of scientists celebrate the culmination of decades of research: a solution to climate change. Then, a gruesome murder – eerily similar to Wilde’s South Pole nightmare – occurs onboard.

Zach goes missing before he can release the DNA results from Kowalski’s murder. Yuto brings Wilde the surprising results of his web search. Olivia escalates her search for the famous scientist.

After another scientist turns up dead, the mole reveals their true identity – and asks for a favor in return.

After the second dose is administered, a team member is stung by a scorpion -- leading the others to discover a whole new level of sabotage has occurred on their base. Two years earlier, Arthur is immediately put through the ringer by Portlaoise Prison's most powerful inmate, Patrick.

Base's supplies are sabotaged. At Portlaoise, Arthur gets a letter from a secret admirer "XX". Distrust mounts over the tampering.

Chaos strikes the base as the trial's computers are infected with ransomware at the same time the participants suddenly begin to get sick. With trust at an all-time low, things come to a head when the root of all evil seems to be unmasked. Meanwhile, Arthur carries out Patrick's dirty work in exchange for access to a cellphone.

When Rachel goes into labor, a brief truce occurs with Maggie, who helps deliver her baby. Shortly after, an unexpected downpour saves them both from dehydration, but only briefly, as the killer ultimately strikes again. Later, the identity of XX is revealed.