Detective Inspector Gabriel Markham tries to track down a serial killer that has ties to his past. DCI Markham finds a break in the case that leads him to a suspect, but he has his own suspicions.

Gabriel faces the prime suspect in the serial murders, but his personal connection to the case places his career in peril. A cat-and-mouse chase reaches its peak, and Gabriel starts to lose control.

Gabriel and the team discover another potential victim of the acid-attack serial killer. Questions surface around Gabriel's suitability for leading the case.

Gabriel and his team plan a risky mission to catch the killer after a tip-off. The killer decides to switch sights towards Gabriel.

The story behind the acid murderer's first victim comes to light as another suspect enters the picture. Gabriel is helped in his investigation by an unexpected source.

When Gabriel finds a crucial piece of evidence, a frantic search for the killer commences. As he picks up on the killer's trail, Gabriel puts everything in jeopardy.