The sixth episode in a major new nine-part conspiracy thriller, starring Romola Garai. Written by Matthew Broughton. As Helen uncovers disturbing details of a dark and illicit industry, she enters territory more vast and dangerous than she could ever have imagined. What was the medical experiment carried out on the boy in the coma? And how does it connect to the plane crash? Tracks: A story in nine parts about life, death and the human brain. Directed in Wales by Helen Perry.