Sid (John Leguizamo), (Ray Romano), Diego (Denis Leary) and the rest of the pack must leave their home to save themselves after Scrat (Chris Wedge) blasts across space in search of the elusive acorn - catapulting out into the universe where he accidentally causes a meteor shower to head straight to Earth, threatening their homeland.
When the meteors crash down on Earth, the friends - along with their new astronomer friend Buck (Neil deGrasse Tyson) - realize they're facing extinction if they can't put a stop to the changes Scrat has instigated. They leave their home and travel together to a crash sight far away in search of clues on how to stop the impending doom.
Amy Mitchell (Mila Kunis) is a mother of two who puts her family first, but her childish husband, demanding kids and idiot of a boss are finally getting to her. One morning as she's making breakfast, she realizes the dog is sick. Now she has to take the dog to the vet in addition to dropping the kids off at school before getting to her high pressure marketing job.
When PTA Queen Bee Gwendolyn (Christina Applegate) at her kids’ school tells her there's an emergency PTA meeting, Amy doesn't feel she can blow it off, so she makes sure to leave work early enough to make it. After an incredibly stressful day, Amy snaps during the meeting. She teams up with two other misfit moms (Kathryn Hahn, Kristen Bell) on a quest to free themselves from conventional responsibilities. They go on a well-deserved binge of freedom, fun and self-indulgence.
Pete (Oakes Fegley) is a 10-year-old boy who has been living in the woods for years. He hasn't been around humans, instead living a peaceful life with Elliot, the dragon who found him when he was four, and the other animals of the forest.
When a forest ranger (Bryce Dallas Howard) spots Pete, she tries to figure out where he came from. Worried for his safety, she takes him in. When he draws a picture of Elliot and claims the dragon is real, she goes to her father (Robert Redford) for advice. For years, he's been telling local kids about meeting a dragon living deep within the forest. Grace tries to get to the bottom of Pete's unbelievable story and his mysterious friend.