The six members of the primitive family Grug live under the protection of their father Grug (voiced by Nicolas Cage). Every day, they snatch ostrich eggs for food, avoid the pursuit of wild beasts, listen to their father narrating the same story every night, and live a monotonous life in the cave. The eldest daughter Eep (voiced by Emma Stone) is a curious girl with a completely different personality from her father. She is not satisfied with staying in this small cave for a lifetime and wants to pursue the new world outside the cave. Unexpectedly, the end of the world suddenly came, the cave was destroyed, and the family was forced to leave their home and embark on a new journey. Leaving the cave where they have lived for "a lifetime", what is presented to them is a brand new, gorgeous but dangerous new world, full of cannibalistic flowers and plants and strange birds and beasts that cannot be named. The family encountered an unprecedented crisis. During the journey, they also met Guy (voiced by Ryan Reynolds), a member of the nomadic tribe. He had extraordinary creativity and innovative ideas, helping the Gulu family to avoid many difficulties. On the way, he also invented many "high-tech" products and let them know that life requires "brains" and walking requires "shoes", etc. The group embarked on a noisy and thrilling journey in the film.