Sonic and Tails befriend a pair of aliens who crash land their spaceship on Mobius. Sonic has to avoid Robotnik's ULTRA-GRAVITIZER (sort of a hedgehog flypaper) to help fix their ship and blast-off back home.
Santa Claus has made an announcement - he is retiring and has picked the perfect successor - "Robotnikclaus"! Sonic and his sister resolve to persuade Santa to return and set Christmas straight. When the two track down the Santa who made the announcement, they discover he is just a phony robot and the real Santa Claus is being held prisoner.
In order to free Sketch Lampoon (a satirical comic book artist) from Robotnik's new high security prison, Sonic allows himself to be captured, then makes a high speed rescue and escape.
The sinister Robotnik blackmails Cyrus, an old friend of Sonic's, by holding his father hostage.
Sleet and Dingo plan to collect the taxes owed to Robotnik from the Duke of Velcronia but keep it for themselves.
Sonia discovers that the watch she received from her friend is actually a monitoring device for the Robotnik Intelligence Agency.
Antoine decides to study martial arts but after he wrecks most of Knothole Sonic sends him off to practice in the woods. //Tails begins his training to become a real Freedom Fighter by learning tracking skills while on a camping trip.
In Part II, Sonic and Sally steal the Roboti-sizer plans, stop the Destroyer from polluting the Great Forest and save Little Sonic, Little Sally and Dulcy's mother, Sabina.
After a disastrous failed mission, Sonic laments that they can't go back and prevent Robotnik's take-over. Dulcy tells them they can and takes Sonic and Sally to the Floating Island where they find the "Time Stones".
Sonic attempts a solo rescue to prevent prisoners from being roboti-sized and is hit by a Memory Scrambler that erases short-term memory.
The Freedom Fighters run into a Swashbuckler, named Ari, battling Swat-Bots. Sonic diverts them, allowing Ari to escape. After hearing that Robotnik is holding his band of Freedom Fighters hostage, Ari decides to help Sonic free them.
Sonic reluctantly takes Tails with him to the Big City to find some cotter pins for the Freedom Fighters catapults. While in the City, Sonic is nearly eaten alive by his old dog Muttski, now a roboti-sized guard dog in the Junk Heaps
Tails brings a new friend home to Knothole - a baby Terra-Pod who has strayed from the herd that is currently migrating. Sonic, Sally, and some of the other Freedom Fighters return the Baby-T to its mom and the rest of the herd.
Robotnik severely upsets the ecosystem above and below the surface, when he sends explosive, Robotnik snake probes drilling deep under ground in search of oil lakes.
Santa Claus has made an announcement - he is retiring and has picked the perfect successor - "Robotnikclaus"! Sonic and his sister resolve to persuade Santa to return and set Christmas straight. When the two track down the Santa who made the announcement, they discover he is just a phony robot and the real Santa Claus is being held prisoner.
When Tails gets trapped in the "Warp of Confusion" (an Escher-like world of another dimension) by Robotnik's cousin, Dr. Warpnik, Sonic comes to the rescue and traps Robotnik and his badniks in the warp.
The Hedgehogs steal historical artifacts of Mobuis from Robotnik before he can pawn them off at an auction.
While lost in the wastelands of Mobius, Sonic, Manic and Sonia stumble upon an oasis called Lake Valley Resort.
A homecoming is interrupted for Sonic, Sonia and Manic when Sleet and Dingo arrive to collect back taxes after returning to their birthplace.
Santa Claus has made an announcement - he is retiring and has picked the perfect successor - "Robotnikclaus"! Sonic and his sister resolve to persuade Santa to return and set Christmas straight. When the two track down the Santa who made the announcement, they discover he is just a phony robot and the real Santa Claus is being held prisoner.