While two care home staff are chasing Kevin McDowd, a young man with learning disabilities and sociopathic tendencies, Nikki and Jack examine a fatal road accident where the deceased is Kevin McDowd's mother. The investigation led by police sergeant Button should be straightforward, but the forensic evidence suggests foul play.

It is Christmas morning and Nikki is awaiting a call from Matt who is back in the States. Instead, she receives a call to say that the team is needed: a family has been massacred at an enormous property owned by Andy McMorris, the CEO of a haulage company.

Greeted by SIO DI Gibbs, Nikki is first on the scene whilst Clarissa is connected to the action via screens and microphones back at the Lyell. Having left his father to celebrate Christmas without him, Jack is just arriving to join them when a gunshot suddenly rings out.

With Gibbs lying on the floor with a life-threatening injury, the team realise that the shooter might still be on the grounds. Are they also in danger?