The discovery of a body in a remote lake leads Mathias and the team to investigate the complicated private life of a missing teacher from a small rural school. What is Gwilym's secret? Who is Ben Willis? Why did another ex-teacher commit suicide? Who is the mysterious girl and why is she hiding from Mathias? Is Greta still alive? This is a world rife with secrets. Will Mathias and the team unravel them in time or is it already too late?.
Aired: 11 Oct 2015