Undercurrent: The Disappearance of Kim Wall tells the story of accomplished journalist Kim Wall, who tragically went missing in 2017. She was last seen just prior to interviewing the eccentric entrepreneur Peter Madsen aboard his self-made submarine in Danish waters. Madsen changes his story multiple times during the course of a police investigation that ultimately uncovers the truth: Wall was murdered on the submarine. Madsen is soon put on trial, and a judge is tasked with determining what actually happened on the vessel.