On Snowpiercer Season 1 Episode 1, Andre Layton is taken uptrain from The Tail to solve a murder that threatens the Order of the Great Ark Train. Cavill has a secret.
Seven years into their perpetual journey, the Tailies on the Snowpiercer have minimal food, no rights, and are being sterilized. Layton and Pike plan to revolt but Layton urges patience while Pike and Josie want immediate action.
Before they are able to enact their plan, Layton is called uptrain and asked to use his skills as a former homicide detective to solve a murder. His ex, Zarah, is one of the suspects as she lived with the victim in a polyamorous relationship with two others.
In The Tail, Old Ivan commits suicide and this sparks Pike to put the revolt plan in action. A massacre ensues, ending in a stand-off with Pike holding Brakeman Till as a hostage. Layton comes back to defuse the situation and convinces the leaders to submit themselves to The Drawers and medically-induced comas so that they can be uptrain when he revives them for the real revolution.
In exchange for this relative mercy to The Tail, Layton agrees to solve the murder. Cavill agrees with the caveat that one significant arm will be taken in the morning as a sign of swift justice for the six brakemen killed in the revolt.
Once work is done for the day, Cavill retires to the Engine to bring dinner to Mr. Wilford. She changes out of her uniform and takes over at the controls of the train where Engineer Ben cedes his seat and addresses her as "Mr. Wilford".
On Snowpiecer Season 1 Episode 1, a murder onboard the Great Ark Train requires bringing Layton, a Taillie and the world's last homicide detective, uptrain to help solve it.