How does Snowpiercer explain the newest survivors?

Audrey's arrival at the conclusion of the season four premiere suggested that in the nine months since Snowpiercer and Big Alice separated, things had gotten continually worse for the train's survivors in comparison to those building New Eden.

Focusing mostly on Melanie, Ben, and the train, "The Sting of Survival" portrays how the regular and ordinary travels take a dangerous turn of events when the train is boarded by peacekeepers intent on taking over the train and forcing Melanie to speak with them, usually by threatening the lives of the other passengers.

While the season premiere focused entirely on how the society had already been built nine months after their departure, Snowpiercer's following episode was all about how these new survivors were introduced.

The episode does the work of explaining that these newly introduced survivors lived underground and were a group of scientists meant to bring the world's temperature higher. However, most of the episode is about Melanie trying to determine how large of a threat this group is, the peacekeepers showing their willingness to kill a hundred of the train's passengers, and trying to fit in an explanation of how these people survived in the first place. "The Sting of Survival" never actually gets the chance to show how these dangerous peacekeepers went from wanting Melanie to allow the train to be used for scientific purposes of heating the Earth back up to the peacekeepers creating a dangerous environment with the intent of causing more harm.

They could be hiding a dangerous ulterior motive or unknown endgame. One episode is not enough to understand the truth of who these new characters are or what they want. However, Snowpiercer does set up various mysteries surrounding who these people are, and any potential dangers they may bring to the train.

Upon realizing that there is a dangerous scheme intended for the survivors in New Eden, Till, Audrey, and Ben enact a plan to send Till out to warn their friends. Except, when a fight breaks out, Audrey must take her place.

"The Sting of Survival: is an episode all about set-up and preparing the audience for what comes next. It is, for the most part, a building block meant to introduce these new characters before the rest of the season allows Layton to confront the train and strive to get his daughter back.

However, confirming for Melanie that those who left for New Eden did survive gives Melanie hope of seeing her daughter again, something that could play into Melanie's motivations as the season goes on.

These first two episodes have laid the ground work, but as the final season continues, it needs to start blending these storylines and characters back together to truly bring this show to a close.