DCS Kat Frank is recently widowed and a single mum to 18-year-old Cam, but she's keen to put her personal life to the side and get to grips with a new case. Then her boss tells her she's the lead in a pilot programme to test an initiative using AI in police work. 

For Kat this is fraught with difficulty on so many levels. She largely holds AI responsible for her husband's death, and she certainly doesn't believe that crimes can be solved by machines, so she takes on the role with her own expectations and agenda. 

Working with AIDE (Artificially Intelligent Detective Entity) Lock, Kat and her team start work on reviewing two missing person's cold cases. Combining logic and gut instincts, years of experience and statistical analysis, the team comes to show that the cases aren't what was first thought. 

They have to act decisively and quickly, overcoming their difficulties in communication, application and understanding. But when Kat is affected personally by events, she finds that the only place she can turn is Lock. 

This is a fantastic book. I really couldn't put it down. The rest of life was on hold until I finished it! The characters were believable, flawed and engaging. The crime was mystifying and ultimately horrifying and shockingly convincing. But above all, the concept of using AI within detective work was fascinating and cleverly presented. So many things to consider in the moral and ethical applications of using machines for investigation, but also how humans treat each other in the light of judgement, prejudice and power.