From the author of the Sunday Times top ten bestseller, The Dry.

'Harper is wonderful at evoking fear and unease' The Times

Five women reluctantly pick up their backpacks and start walking along the muddy track. Only four come out the other side.

The hike through the rugged landscape is meant to take them out of their air-conditioned comfort zone of the office and teach resilience and team-building. At least that's what the corporate retreat website advertises.

Police officer Aaron Falk has a particularly keen interest in the whereabouts of the missing walker. Alice Russell is the whistleblower in his latest case - and Alice knew secrets. About the company she worked for and the people she worked with . . .