A woman park ranger has an accident during a survey of New Mexico's Carlsbad Caverns, a 300-mile labyrinth of caves and tunnels 800 feet underground. Fellow park ranger Anna Pigeon braves her claustrophobia to mount a rescue and discovers it was no accident
Visiting an isolated Lake Superior isle to study wolf behavior, ranger Anna Pigeon joins a scientific group that subsequently discovers unusual DNA evidence suggesting that a giant and dangerous wolf hybrid has been introduced by an unknown source.