DCI Ross Tanner of the Specialist Elite Murder Unit is working on a case with ambitious DI Catherine Tully when he makes the frightening discovery that he is slowly losing his sight. Tully agrees to cover for him but under certain conditions.

Despite learning of his impending blindness, Tanner perseveres on the case; when Tully realises Tanner's secret, she decides to cover for him, under specific conditions.

As the case progresses, Ross's erratic behaviour increasingly alienates him from his team, and Catherine becomes more than just his eyes. The sudden reappearance of Adam Bendrix, the victim's mysterious step-uncle, causes a stir.

Tanner and Tully have a surprising breakthrough about Matthew's stepfather.

Tanner investigates an unsolved case of a murdered violinist named Vicky Ingham, whose nine-year-old son had been found next to her body, and is the key witness to the murder.

Tanner recreates the scene of the vicious murder of Vicky Ingham, but conflicts arise within the unit because he decides to use her young son, who is the key witness, to aid in the process; Tanner's moves come under close scrutiny from DI Boyd.