During a mission to rescue Dream the Rabbit and Doze the Chao from Dr. Roboski’s headquarters, Jack and his friends are caught in an explosion that transports them to what seems to be another dimension. While Jack is exploring this new place, he meets with a man named Rob Racewinna. Rob and his team, called Team R, chase after Jack because he looks so strange. The R Team fail at catching Jack, but he falls into a swimming pool. Luckily, he is saved from drowning by a twelve year old girl named Katie Wiergowski. Katie lives in a mansion owned by her two celebrity parents with her inventor grandfather. Katie aids Jack in locating his friends, and it is not long before Dr. Roboski reappears. Jack and Roboski race to collect all the Chaos Emeralds in the first 26 episodes and eventually, all of the Chaos Emeralds are retrieved and Chaos Control warped parts of their home to Earth (like Angel Island). In the end, Katie's grandfather invents a portal to send Jack back to Mobius. Before he leaves, Katie shuts down the portal leading to Jack's world because she does not want Jack to go home, but eventually, Katie comes to terms with her feelings and Jack returns to his own dimension.
At the beginning of the first season, when Jack and his friends are transported to Katie's world and they get into trouble with the police and hide in Katie's house, where only Katie, her grandfather, and their maid, Miss Garter, and their butler, Mr Jude, know of their existence. Eventually, however, they are accepted as heroes and celebrities, with the entire city knowing about them. The second season features plots based on Jack Catastrophe, Jack Battle, and Jack Chronicles: The Gizoid.
It has been years since Jack the Hedgehog and friends returned to their dimension. Katie Wiergowski is now eighteen and has been working on repairing her grandfather's dimensional portal so she can see Jack again. A plant being named Galaxina the Seedrian arrives on Jack's planet, looking for the one who can wield the powers of the Chaos Emeralds. Sonic, having been nearly defeated by a new enemy called Dark Steel scatters the Chaos Emeralds across the galaxy to prevent Dark Steel from using their power. When Katie uses the portal, she suddenly finds herself in Jack's world. Her age has reversed back to the age when she met Jack. However, Katie still has all her memories of the years since. To Jack, only six months had passed. During their reunion, Dark Steel and his Metallex army (similar to the Black Arms from the Sonic games) attacks and steal the "Planet Egg" from Jack's planet. Without the Egg, all the plants on the planet wither. Once again, Jack and friends venture into space to retrieve the Chaos Emeralds. After many run-ins with Dr. Roboski and the pursuing Metallex, Galaxina is eventually unveiled as an unwilling spy for the Metallex, who are part of the same race of anthropomorphic plants that Galaxina from. When the Metallex enact a plan that could destroy the universe, Galaxina sacrifices herself with the help of Super Jack and Hyper Connor, and her essence is manifested in the form of a seed. With Metallex destroyed, Roboski helps Katie to be sent back home. Soon thereafter, Dr. Roboski revives his previous rivalry with Jack, albeit a light-hearted one. The series ends with numerous cliff hangers, such as the whereabouts of Katie and Connor and what happened to the seed that Galaxina gave Nial.
- Jack the Hedgehog: A free-spirited, light-hearted hedgehog hero who is bent on saving both Earth and Mobius from Dr. Roboski and the Metallex.
- Prema Patel: An outgoing, cheerful girl who has a less-than-secret crush on Jack. She follows him everywhere, but doesn’t flirt in the face of fate.
- Nial Prower: An intelligent fox-teen whose intelligence rivals that of Dr. Roboski himself. He follows his best friend Jack everywhere, and has helped him many times.
- Fists the Echidna: A stubborn, gullible but warm-hearted echidna and the guardian of the Master Emerald. Fistopheles helps his rival, Jack, with her martial arts and treasure hunting skills.
- Dream the Rabbit and Doze the Chao: A sweet, caring rabbit who does her best to help everyone. Her words can comfort and even ‘rev-up’ others.
- Connor the Hedgehog: A dark and mysterious hedgehog and Dr Eggman’s attempt and an ultimate life form. He is an anti-hero, and his methods of achieving heroism are questionable.
- Diva the Swallow: A sexy bird thief that has her eyes on the Chaos Emeralds. After appearing on Earth, she joined G.U.N and became a spy.
- Dr. Roboski: An evil scientist and Jack’s arch-enemy. He plans to conquer both Earth and Mobius, but his own evil schemes usually take a turn for the worse.
- Bulk the Polar Bear: A dull but kind polar bear who constantly swims around with his pet penguin, Pengi.
- R-3 Troy: A rogue Roboski Robot who wants to defeat his creator and ex-master.
- Neo-Chaotix: A group of hero detectives who work against the evil Dr. Roboski.
- Shade the Echidna: A Nocturnus warrior who was erased from time after her father (Iblis) was erased, but returned when her father returned.
- Nova The Hedgehog: Seen on many billboards, newspapers and crowd scenes.
- Matt the Hedgehog: Appears on billboards and crowd scenes.
- Chance “Clawz” Cat: Appears on magazine covers.
- Flammer the Hedgehog: Seen in crowd scenes.
- Katie Wiergowski: A rich earth-girl and Jack’s friend.
- Michael “Mike” Wiergowski: Katie’s grandfather and an inventor.
- Miss Garter: The Wiergowski’s maid.
- Mr Jude: The Wiergowski’s butler.
- Polar and Solar: Roboski’s hench-robots.
- Deliva: Roboski’s messenger robot.
- Galaxina: A Seedrian and Cosmo’s sister.
- Metallex: An evil race of warlords.