DI Chambers and her partner DS Dhillon investigate an elusive serial killer named Gideon Shepherd.

Lucy and Gideon identify a suspect in their efforts to prevent an atrocity. Lucy risks everything to confirm her suspicion, culminating in a decision she will never be able to come back from.

Lucy desperately tries to cover her tracks as secrets and lies are forced into the open and a terrible deadline looms.

Lucy confronts the reality of her situation and is forced to make an impossible choice. Boyd is tested to her limits in her pursuit of the truth, and Dhillon comes to a realisation, with catastrophic results.