Melanie crosses a snowy landscape on a volt-sled. It gets stuck within sight of the weather station and she's left to drag a trailer flat of necessities the remaining distance. Her suit's battery is nearing depletion as she arrives.
She starts to dig access to the door and hits something buried in the snow. She uncovers a body with a bullet wound in the head.
She gets the door open and gets inside. She connects to the battery supply and starts to recharge her suit.
Inside the station, she finds the body of a woman who had committed suicide in the freeze and remembers moments from her Night Car reconciliation with Alex.
She erects a thermal tent and turns on a heat lamp. She starts a journal.
She goes outside to clear off the solar array and comes across another body. In the morning, she moves the woman's body outside too.
She patches her batteries into the solar array and when she gets the switch to flip, they start recharging, and the life support systems kick on.
She feels a rumble in the earth and when she heads back to get her sled with the rations, she finds it buried under an avalanche.
Flashback to the completion of Snowpiercer. Wilford crows over the accomplishment, loathe to share any of the credit with Melanie.
In the station, Melanie unpacks what rations she does have and starts to calculate what she can afford to eat daily. Including a treat from Ben. She searches the station's kitchen for any food and finds a human arm in the fridge.
A hallucination of Wilford appears, taunting her in her exhaustion.
Melanie plans out her month of isolation and begins a routine of maintaining the solar panels and getting the equipment running.
Wilford continues to spar with her verbally as she prepares to uplink to the first weather balloon.
She opens a ration biscuit pack and metes out her allowable portion. Contact with the first weather balloon is made.
She wakes up and finds her biscuit plate empty. Wilford questions her sanity.
Flashback to preparations for Snowpiercer. Melanie confronts Wilford over the Night Car. She argues for including geneticists instead of jackboots.
He threatens to leave her family behind if she doesn't fall in line.
Ten days since Melanie arrived at the weather station and Melanie has data from seven weather balloons and is working on a climate model. Her food has run out.
She starts hallucinating Layton who reminds her that the Tailies suffered hunger often. He reminds her she has two bodies lying out in the cold.
Hearing a noise in the station, she investigates and discovers there are rats. Using a piece of the body outside as bait, she creates a rat trap.
Melanie discusses the three bodies with her hallucination of Wilford.
Flashback to the night of Snowpiercer's departure and the Tailies rushing the fence to try to board. Melanie's waiting for word on her family and Wilford is angry at the chaos downtrain. He orders Gray to do whatever it takes to hold them back, authorizing all necessary force.
Ben gives him an excuse to hold the train's departure by thirty minutes. A group of scientists approach the engine, stopped by armed security.
Melanie wakes up when her trap catches a rat. She dip it in a pot of ink and lets it run. She tracks it to a hole in a wall. Tearing the wall out, she finds a geo-thermal vent where the rats have survived The Freeze.
A hallucination of Alex appears to explain the vent.
Melanie cooks a rat for a meal and talks things out with Alex.
Flashback to the confrontation with the scientists. Wilford orders them all shot so they can get the train going. Melanie is in shock when Wilford states that he's going downtrain to deal with the Tailie-wannabees.
Wilford takes a Jeep to drive downtrain.
In the station, as Melanie awaits the uplink to the last balloon, a windstorm outside damages a tower, causing it to breach a glass panel. Melanie rushes to seal it with a foam gun. She goes outside to inspect the damage. When she returns, the balloon data's been wiped.
Wilford's spectre continues to taunt her with suggestions of suicide and reminding her how she abandoned Alex.
After a momentary lapse, Melanie goes back out to repair the tower. She falls as the lever falls apart.
Flashback to Snowpiercer's departure. The Tailies are rushing the train and Melanie is trying to get confirmation of her family boarding the train. Wilford contacts the engine to inform them that he is returning uptrain by Jeep. Ben insists that Melanie order the train to go before Wilford returns. In tears, Melanie engages the engine and Snowpiercer departs.
In the present, Melanie gets up and manages to get the tower back up just as her suit loses power.
With the tower up again, the balloon data links back up.
Melanie waits out the last weeks and tries to contact Snowpiercer as the date of return approaches. There is no response and the date passes. The Alex hallucination returns and absolves her of her choices. Alex transforms into her eight-year-old self as Melanie cries.
Rousing herself, Melanie feels the vibrations of the approaching train. She loads her sled and makes her way to the track, radioing that they need to slow. There is still no response and the train speeds past her, Alex's desperate face in the back engine window, crying out to her as they pass.