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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.

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.

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.

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.

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.