US Park Service investigators Doug and Jill Fletcher are dispatched to Hawaii when the bodies of two hikers are discovered near the Kīlauea volcano. Initially reluctant to accept the assignment, Doug becomes intrigued when he learns that the investigating ranger's report of lost hikers overcome by volcanic gasses disagrees with the autopsy findings. As the investigation progresses, the Fletchers find themselves entangled in more than the investigation of the death of two park visitors.