Prehistoric fantasy. Twelve-year-old Pitt and his pterodactyl pal Kantrop try to help their tribe. A huge chasm opens up, dividing the village in two, with tribe members on each side. Pitt invents the postal service with Kantrop, to transmit spoken messages and parcels to each side. He then engineers the building of a bridge to join both halves before they declare war on each other because of miscommunication. Meanwhile, Grenella has fallen into the chasm. Will they notice her in time to save her?