This is a fact: Ryan Summers walked into Three Rivers College and killed 13 women, then himself. But no one can say why. The question is one that cries out to be answered - by Ryan's mother, Moira; by Ishbel, the mother of Abigail, the first victim; and by DI Helen Birch, put in charge of the case on her first day at her new job. But as the tabloids and the media swarm, as the families' secrets come out, as the world searches for someone to blame...the truth seems to vanish.

In the shadow of the Pentland Hills, a man has been callously struck down in front of his home. Tyre marks suggest it was no accidental hit-and-run. Somebody wanted him dead and as the man fights for every breath, they might still get their wish. Grappling with the demons he thought he could leave behind after months away on enforced leave, D.S. Malkie McCulloch resists pressure from his superiors to pass the case on to the road policing unit, convinced that whoever was behind the wheel will be waiting for the chance to finish the job.

Hogmanay. New Year's Eve. A dead teenager, another missing. One hell of a case. Meet DS Vicky Dodds. Settling down for a nice Hogmanay with her daughter and her best friend, a phone call pulls DS Vicky Dodds into work and to a deadly new case. A teenage girl, her body cooling in a cold, dark supermarket car park. Found next to her friend’s car, but the driver’s missing too — has the killer taken her? Or is she the killer?

A woman is found in a local cemetery, crushed to death under a gravestone. A production company is there, filming the remake of a classic sci-fi TV show on the grounds, making the investigation more difficult for DCI Harry McNeil. It's his first day in charge of the cold case unit in Edinburgh. After spending four years in Professional Standards, he has little choice but to take the promotion.

While her parents are just yards away, thirteen-month-old Lily Hamilton is abducted from Ayr beach in Scotland. Three days later, her distraught father turns up at private investigator Charlie Cameron's office. Mark Hamilton believes he knows who has taken his daughter. And why. Against his better judgment, Charlie takes the case—and when bodies are discovered, he suspects this may not be an isolated crime. Is there a serial killer whose work has gone undetected for decades? Is baby Lily his latest victim?