Taking a late night stroll to clear her thoughts and get a new perspective on a string of missing persons cases she had been investigating, Detective Zoe Sutton finds herself alone in the woods watching a group of men lead two women into the Depths – a once beautiful cave system that had been closed due to safety concerns, with no gun for protection or phone to call for backup. Attempting to follow them in, she soon finds herself wrapped up in the perverse world of sexual depravity.