Fiona Wagner, a journalism master's student, mourns her mother's suicide while her father, Detective Tom Wagner, investigates the death of a lawyer killed by his own daughter under threat from a sadistic criminal. When a pianist is forced to choose between losing his hearing or his fingers, Tom realizes a deranged serial killer is on a rampage. Meanwhile, Fiona is contacted by the criminal, ISO_17, triggering her investigation into her mother's cryptic suicide note.