Story
The story of Knuckles' Chaotix varies between the Japanese and Western releases of the game, with completely irreconcilable storylines separating the two.
Japanese
A mysterious island rose from the southern sea a few months after the events of Sonic & Knuckles. Dr. Eggman discovered the island, and found a mysterious little ring inscribed with text dating from a legendary civilization. Soon after, Eggman found another ancient ring resembling one of the Super Rings of the Floating Island, which turned out to be the Special Ring once used by that lost people. The mysterious space the Special Ring created was filled with the Master Emerald Pillar's energy, which crystallized into six Chaos Rings. After this phenomenon, Eggman decided to continue the investigation of the Special Ring in order to uncover the secrets of the rings used by Sonic and friends, as well as to theoretically summon the coveted Master Emerald. Inspired, Eggman quickly converted the island into a resort he dubbed Newtrogic High Zone, serving as his high-tech research fortress. He crystallized energy into artificial Dark Rings for his machines, and began to develop Ring Power, which would create a space-time connection between Rings. Mighty the Armadillo, Espio the Chameleon, Vector the Crocodile, and Charmy Bee all arrived at the island for different reasons, and ended up being captured and placed in the Combi Catcher machine by Eggman and Metal Sonic. Knuckles the Echidna, deducing that something was amplifying the power of the Master Emerald Pillar, also headed to the island and managed to rescue Espio along the way. The two then make their way to the World Entrance where they find the others, and go on to stop Dr. Eggman from succeeding in his plans.
Western
The plot starts out on the day before the opening day of Carnival Island, a huge amusement resort with the latest in high-tech rides and games. As the guardian of the island, Knuckles' job was to make sure nothing went wrong before the grand event.
Behind the scenes, however, Dr. Robotnik was cooking up a new dastardly scheme. To fuel his latest diabolical device, Robotnik went to Carnival Island to find the Power Emerald that supplied electricity to the entire island- a tool which would fit into his plan perfectly. To further ensure that Knuckles and his friends would not interfere with his plans, Robotnik used his Combi Catcher to freeze Mighty the Armadillo, Espio the Chameleon, Vector the Crocodile, and Charmy Bee in time.
When Knuckles returned from patrolling the far end of the island, he found Dr. Robotnik as he was imprisoning Espio the Chameleon in a Combi Catcher, scaring the villain off and rescuing Espio. After that, Knuckles discovered that he could rescue his other friends one at a time by using Ring Power, a power that holds two partners together like a magical rubber band. Never held back for long, Knuckles set out with his team to save Carnival Island from Robotnik before the grand opening.
