原始人咕噜一家六口在老爸Grug（尼古拉斯·凯奇 Nicolas Cage 配音）的庇护下生活。每天抢夺鸵鸟蛋为食，躲避野兽的追击，每晚听老爸叙述同一个故事，在山洞里过着一成不变的生活。大女儿Eep（艾玛·斯通 Emma Stone 配音）是一个和老爸性格截然相反的充满好奇心的女孩，她不满足一辈子留在这个小山洞里，一心想要追逐山洞外面的新奇世界。
Grug：That was too close!
Eep：I was watching. I was fine.
Grug：What were you doing up there, Eep?
Grug：Well then, why did you go up there?
Eep：I don't know!
Grug：Why don't you know? Stop looking for things! Fear keeps us alive, Eep. Never not be afraid.
Eep：What's the point of all this?
Grug：What was that?
Eep：I mean, why are we here? What are we doing this for?
Grug：No one said survival is fun.
Eep：Nothing is fun.
Grug：Would you come down here?
Grug：I just don't see why she needs her own ledge. That's all. That's what this is about.
Ugga：She's working through some things and needs some space.
Grug：What things? How long is this going to take? Really? She already doesn't listen to me. Hey!
Ugga：See? She's listening.
Grug：If she wants to survive, she has to follow our rules.
Ugga：How about a story? Eep loves those.
Grug：That's a good idea. How about a story, huh?
Gran：Yeah, tell us a story.
Grug：Okay. Can I borrow that? Thank you. Eep! Your old favourite!
Eep：I haven't played with that thing in years.
Grug：Tonight we'll hear the story of Krispy Bear. A long time ago, this little bear was alive. She was alive because she listened to her father and lived her life in routine and darkness and terror. So she was happy. But Krispy had one terrible problem. She was filled with... curiosity.
Grug：Yes, yes. And one day, while she was in a tree, the curious little bear wanted to climb to the top.
Grug：And no sooner had she climbed to the top she saw something new and died.
Thunk：Just like that?
Grug：Yes! Her last moments of terror still frozen on her face.
Gran：Same ending as every day.
Thunk：I get it, Dad. I will never do anything new or different.
Grug：Good man, Thunk.
Ugga：All right, everyone sharpen your teeth and let's pile up.