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。
Guy：Looks like we won't have any leftovers.
Eep：What are leftovers?
Guy：You know, when you have so much food to eat you have some left over.
Eep：Well, we never have that much food.
Ugga：Grug, how about a story?
Grug：That's a good idea. How about a story, huh?
Thunk：Yeah, a story! Tell us a story!
Grug：Once upon a time there was a little tiger who lived in a cave with her family. There were a lot of rules, but the big, simple one was to never leave the cave at night. And the door was so heavy, Do you think it would be easy to remember.
Thunk：So easy to remember.
Grug：I know. But while everyone was asleep, she went out anyway.
Grug：Yes! And no sooner than she did her cave was destroyed and everyone had to go on this long, sucky walk, with some weirdo they met, and died! The end.
Guy：I did not see that coming. My stories never end like that.
Thunk：Yes! Two stories in one night!
Guy：Okay, but it won't be as good as Grug's. Once upon a time, there was a beautiful tiger. She lived in a cave with the rest of her family. Her father and mother told her: "You may go anywhere you want, but never go near the cliff, for you could fall.
Grug：And die. Good story.
Guy：But when no one was looking, she would go near the cliff, for the closer she came to the edge, the more she could hear, the more she could see, and the more she could feel. Finally she stood at the very edge, and she saw a light. She leaned to touch it, and she slipped.
Grug：And she fell.
Guy：And she flew.
Thunk：Where did she fly?
Guy：A place with more suns in the sky than you can count.
Thunk：It would be so bright.
Guy：A place not like today, or yesterday. A place where things are better.
Grug：Tomorrow isn't a place. It's... It's... It's... You can't see it!
Guy：Oh, yes it is. I've seen it. That's where I'm going.
Grug：Well, we are going to shut our eyes and sleep. And when we wake up, we're going to find the place that has everything we want.