If you really don't go to the movies, you won't see...
An orphan with terrible aunts for guardians, befriends human like bugs who live inside a giant peach, who take the boy on a journey to New York City.
In the 1930s, James Henry Trotter is a young boy who lives with his parents by the sea in the United Kingdom. On James' birthday, they plan to go to New York City and visit the Empire State Building, the tallest building in the world. However, his parents are later killed by a ghostly rhinoceros from the sky and finds himself living with his two neglectful aunts, Spiker and Sponge.
He is forced to work all day and they threaten him with beatings to keep him in line and taunt him about the mysterious rhino and other hazards if he tries to leave.
While rescuing a spider from being squashed by his aunts, James meets a mysterious man with a bag of magic green "crocodile tongues", which he gives to James to make his life better. The soldier warns him not to lose the "tongues" and disappears. When James is returning to the house, he trips and the "tongues" escape into the ground.
A peach is soon found on a withered old tree, and expands into immense proportions. Spiker and Sponge then use the giant peach as an attraction, making lots of money as James watches from the house, not permitted to leave. That night, James is sent to pick up the garbage. While doing so, he grabs a chunk of the peach to eat as one of the "crocodile tongues" unknowingly jumps into it. A large hole appears inside the peach and James crawls inside, where he finds and befriends a group of life-size anthropomorphic bugs who also dream of an ideal home (Grasshopper, Centipede, Earthworm, Miss Spider, Ladybug, and Glowworm), and is also turned into a more animated form. As they hear the aunts search for James, Centipede manages to cut the stem connecting the giant peach to the tree and the peach rolls away to the Atlantic Ocean with James and his friends inside it, seemingly crushing Spiker and Sponge's antique car as they try to chase it.
Remembering his dream to visit New York City, James and the insects decide to go there with Centipede steering the peach claiming he sailed the world as a "Commodore". They use Miss Spider's silk to capture and tie a hundred seagulls to the peach stem, while battling against a giant robotic shark. They escape just in time. While flying, James and his friends eventually find themselves hungry and soon realize that "their whole ship is made out of food". After gorging most of the inside of the peach, Miss Spider, while using her web to tuck in James, reveals to him that she was the spider he saved from Spiker and Sponge. James then has a nightmare of him as a caterpillar attacked by Spiker, Sponge, and a spray the aunts used that resembles the rhino. When he wakes up, he and his friends find themselves in The Arctic, lost and cold. The Centipede has fallen asleep while keeping watch, resulting in them drifting further away from their expected destination. It is then revealed that the Centipede has never traveled the world and has lived on two pages of the National Geographic. After hearing the Grasshoper wishing they had a compass, Centipede jumps off the peach into the icy water below and searches a sunken ship for a compass but is taken prisoner by a group of skeletal pirates. James and Miss Spider rescue him and the journey continues.
As the group finally reaches New York City, a storm appears. A flash of lightning reveals the rhino approaching them. James is frightened but faces his fears and gets his friends to safety before the rhino strikes the peach with lightning; The strings keeping the seagulls attached to the peach break and James and the peach both fall to the city below. James coughs up the crocodile tongue as he reawakens, transforms back into his normal form, and emerges from the peach realizing it has landed directly on top of the Empire State Building.
After being rescued by police officers, firefighters, and the largest crane in New York City, Spiker and Sponge arrive, supposedly having driven their car across the seabed, and attempt to claim James and the peach. James stands up to Spiker and Sponge, revealing their abusive behavior towards him to the crowd, who gasp in shock at the revelation. Spiker and Sponge become enraged by James' betrayal and attempt to kill James. Using the remaining seagulls, the bugs arrive in New York City. They tie up Spiker and Sponge with Miss Spider's silk and the two aunts are taken away. James introduces his friends and allows the children of New York to eat up the peach.
The peach pit is made into a house in Central Park, where James lives with the bugs and has the friends he could wish for. Centipede runs for the Mayor of New York City, Grasshopper becomes a professional violinist, Earthworm becomes a mascot for a new cream, Ladybug becomes an obstetrician, Glowworm lights up the Statue of Liberty, Miss Spider owns a nightclub called "Spider Club", and James celebrates his 9th birthday with his new family.
In a post-credits scene, a new arcade game called "Spike the Aunts" is shown, featuring the rhino.