Five women reluctantly pick up their backpacks and start walking along a muddy track.

Only four come out on the other side.

The hike through the rugged Giralang Ranges is meant to take the office colleagues out of their air-conditioned comfort zone and encourage teamwork and resilience. At least, that's what the corporate retreat website advertises.

Federal Police investigator Aaron Falk has a keen interest in the whereabouts of the missing hiker, Alice Russell. Because Alice knew secrets, about the company she worked for and the people she worked with.

The four returning women tell Falk a tale of fear, violence and fractured trust during their days in the remote Australian bushland. And as Falk delves into the disappearance of Alice, he begins to suspect some dangers ran far deeper than anyone knew.