Obsessed with his hunt for a serial killer, DCI Gabriel Markham's life becomes intrinsically bound to that of his suspect.

Gabriel comes face to face with the prime suspect in the serial murders, but his deep, personal connection to the case puts his career in jeopardy; as a dangerous game of cat and mouse ramps up to its climax, Gabriel begins to lose control.

Gabriel and the team deal with the discovery of another possible victim of the acid-attack serial killer; questions are raised about Gabriel's suitability to be leading this case.

An unexpected tip-off convinces Gabriel and his team to launch a risky mission designed to catch the killer in the act; as the pressure mounts, Gabriel begins to push away those closest to him.

As Gabriel’s investigation is lent a helping hand, the story of the acid murderer’s first victim is revealed, and another suspect enters the frame.

Following Gabriel’s discovery of a crucial piece of evidence, the hunt is on to track down the killer as the truth is finally pieced together.