Plot

Eep (Emma Stone) is a girl in a family of Neanderthal Cavemen (Homo sapiens Neanderthalensis) living and hunting in Pre-historic times, talking about how her family is one of the few to survive nearby, mainly due to the strict rules of her overprotective father, Grug (Nicholas Cage). When in their cave home, Grug tells a story to the rest of the family which includes his wife Ugga, his daughter Sandy, his son Thunk, and his mother-in-law with a character that mirrors Eep's curious nature. He uses this story to warn the family that exploration and 'new things' pose a threat to their survival and says to never not be afraid. This irritates the bored and adventurous Eep, and when the family falls asleep after dark, she ignores her father's advice and leaves the cave when she sees a light moving outside the cave.

Seeking the light's source, she meets Guy (Ryan Reynolds), an intelligent cave-boy (Homo sapiens sapiens). She becomes fascinated with the fire he manages to create and is eager to learn more. He tells her about his theory that the world is reaching its 'end' and asks her to join him. She refuses and Guy leaves, but not before giving her a noise-making shell to call him if she feels the need for help. Shortly afterwards, Eep is then caught by Grug (who had been frantically searching for her) who brings her back home, planning to keep her in the cave for the rest of her life. He is joined by the rest of the family, who Eep then tells them about Guy and shows them the shell given to her, only for them to destroy it in fear of 'new things'. An earthquake then occurs, sending everyone running for the cave, only to be stopped by Grug moments before the cave is destroyed by falling rocks. When they climb over the wreckage to discover a land with lush vegetation, much different from their usual surroundings of rocky terrain. Grug takes his family into the deep forest to find a new cave.

While becoming aware of their new surroundings, the family are chased by a "Macawnivore" (a large, macaw colored Machairodont later called 'Chunky') and attacked by a swarm of "Piranhakeets" (deadly red-furred, piranha-like birds). In an act of panic, Eep sounds a horn similar to that which Guy gave her. Guy hears this and rushes to her. Thinking quickly, he creates a torch of fire, which scares the birds away. The rest of the family are then captivated by the fire, having never seen it before. They steal Guy's torch and accidentally set the land around them in flames. Some giant corn is also lit, which rockets up to the sky, prompting a display of fireworks and covers them as popcorn. After feeling impressed with Guy's intelligence and mind of 'ideas', Grug bottles him in a hollow log to carry him in, then suggests that they take solitude in the cave of a nearby mountain mentioned by Guy. Guy is forcibly persuaded to lead the way, and soon begins to learn of the Croods' way of living, which he thinks of as unusual.

After an unsuccessful hunting attempt, Guy along with his 'pet' sloth, Belt (Chris Sanders), as well as Eep, build a puppet to fool and lure nearby animals. Having captured something afterwards, the family greedily devours everything they caught. Guy and Eep are more sparing. The others realize their greediness and stop eating. Grug then tells another of his morale-lowering tales, this time mirroring the events of their day, mentioning a girl Grug and Ugga had before Eep was born who did venture away from her cave and died. Guy then tells a story of his own, about a paradise he nicknames "Tomorrow".

The next day, the family reaches a path coated in spiked rocks. A freed Guy then presents one of his various inventions called shoes. He makes some out of all the resources he can find, for each family member. This gains him some respect from the others, except for Grug, who starts to feel jealous of Guy's cleverness. After a slew of Guy's ideas help the Croods on their continuing journey, all the family members gain something.

Ugga, her mother and Sandy have their first idea to get past carnivorous plants (which showed what Ugga looked like without her hairband), Thunk encounters a crocodile-like dog who he calls Douglas (and later teaches him to roll off a tree), Eep and Guy grow closer together, while Grug is stranded in a ravine, forcing Ugga to go back for him. They all reach a tree to stop for another night-except for Grug, who feels distraught by his family abandoning his traditions of 'Yesterday' for Guy's traditions of 'Tomorrow.' The next day, a 'desperate' and left-out Grug shows the others some of his ideas, which all end up failing and humiliating himself. They soon reach the mountain, where Grug is unable to convince the family that settling in nearby cave is a better option, reaches to full anger, and proceeds to attack Guy. The two become stuck in tar and Guy reveals his family died drowning in it, and their last words inspired his traditions of "Tomorrow." Grug has a change of heart towards Guy, before he and Guy use a trap to use Chunky to free themselves.

As they are about to reach their destiny, an earthquake opens a deep ravine in their path. Grug throws each of them across the gap and reconciles with Eep but is left behind. He takes shelter in a cave and makes a torch. After seeing a large blank rock face, he paints a large cave-drawing of the Croods and Guy together.

He then encounters Chunky, who proceeds to attack him until the torch is accidentally blown out, panicking them both. The newly reformed Chunky lies near Grug where he has an idea. He then uses a skeleton carried by the Piranhakeets to transport himself, Chunky, Douglas, and several other animals across the ravine barely escaping the oncoming "end" destruction. He and the whole Crood family settle down in a paradise-like environment, and Grug invents the first hug with Eep. Grug becomes less protective, letting the family be more adventurous and risk-taking, and gaining some pets, thus bringing happiness to them all and ride out towards the sun for "Tomorrow."