A mother and her children murdered. A nanny on the run. A killer in pursuit.

Hunted and reviled, ex-nanny Joanne Mason turns to her sister, Detective Karen Ratcliffe. Torn between duty and family, Ratcliffe asks Tess Grey and her partner Nicolas 'Po' Villere to bring Joanne in safely.

A winter cyclone forces Joanne into hiding on the Canadian border - but she can't stay put for long. In close pursuit, Tess and Po head north into the heart of a storm, but they're not the only ones: the real murderer is also hot on Joanne's trail, trying to kill the only living witness to their crime.

As the chase progresses it grows apparent that Joanne couldn't have been responsible for the murders . . . but the heat isn't off her. Some people think she might be a co-conspirator, not the terrified witness she is . . . and when the shocking truth behind the gruesome murders comes to light, Tess and Po have their work cut out to keep Joanne - and themselves - alive!