With their camp threatened by a murderous tiger, Jane sees a chance for gender equality, while Gary invents - underwear. Also, they discover fire.

After a rainstorm soaks the campsite, Jane leads a group, including a woefully unprepared Gary, on a dangerous quest to find dry wood. This leaves Marsh with a captive audience, and a chance to share the greatest story ever told.

Gary sets out to define humanity's first relationship, while Minerva tries to arm everyone in the camp with spears.