Federal police detectives Aaron Falk and Carmen Cooper investigate money laundering facilitated by Daniel Bailey at his firm, Bailey Tennants Finances. They coerce employee Alice Russell to obtain evidence, in return for immunity for her previous embezzlement from the firm. Alice attends a corporate hiking retreat in the fictional Victorian Giralang Ranges with four other employees: her boss and Daniel's wife Jill, childhood friend Lauren, and sisters Brianna "Bree" and Bethany "Beth". Three days later, Falk receives an incomprehensible call from Alice. He then learns that only Jill, Lauren, Beth and a spider-bitten Bree have emerged from the wilderness; Alice is missing. In flashbacks, it is revealed that Falk’s mother also disappeared from the same area during a family hiking trip in his childhood. After searching for several days, Falk and his father found her mortally injured. Falk questions Alice's hiking partners. They recount how during the hike, the group had become lost. A fight over their only map then caused it to fall into a river. Without the map, the group disagreed over which direction to proceed. Alice intentionally misdirected the group against the consensus opinion, causing further tension. The next day, the group discovered an abandoned cabin. Alice suggested this could have been the base of a notorious serial killer active in the area several decades prior. However, the group dismissed her concerns and voted to spend the night there, where another fight ensued. The next morning, the group was awoken by Bree's cries of pain from a spider bite. Finding Alice missing, they proceeded without her and were rescued from the wilderness.