It looks like you're asking for a story summary or recap for Snowpiercer Season 1, Episode 3, specifically the version (which just indicates the video quality/source).
The episode’s title becomes clear: physical access cards are the only currency that matters. Layton discovers that Sean’s murder wasn't random. Sean was a "Jackknife"—a smuggler who helped people move between classes. He had been stealing access keys to the mysterious "Drawers" (a hidden cryo-section of the train). snowpiercer s01e03 720p web-dl
Layton has been promoted to Detective —a title with no real power. He is given a small closet to sleep in near Third Class, a token uniform, and a permanent escort, Osweiller (a brutal, loyal "Brakeman"). Layton isn't solving the murder of Sean (the tailor) to find justice; he's a pawn in a larger game. It looks like you're asking for a story