An Impossible Silence - S1.E11

Laura, a deaf-mute tunnel dweller, witnesses the murder of a police officer, for which another man is framed. She goes above with Catherine, but is kidnapped by the real murderers, who are also police officers. Cuffed to a pipe in the basement of the murderer's house, Laura taps out an SOS, which is heard by Pascal and Vincent rescues her. She decides to return Above to live.