The band visit the Floating Island in search of their mother. There they meet Knuckles the Echidna, the island's guardian, who has been falsely told by Sleet and Dingo that the Sonic Underground is after the Chaos Emerald, and he jumps to conclusions. So while Knuckles and Sonic do battle, Sleet and Dingo set their eyes on the Emerald...
The Oracle, wishing to test the Hedgehog's practical capabilities, strips them of their powers and sends them into an alternate, Roman-themed reality where a Sleet-look-alike presides as King. The former fast and furious hedgehogs must use their usual blend of cunning and strategy to save this reality, but without their super-speed, will they be stopped dead in their tracks?
Using the essence of a rare plant, Robotnik manages to make Sleet and Dingo fast-- maybe even faster than Sonic. The Sonic Underground manage to get hold of it, but can Sonia and Manic resist the temptation of taking the potion themselves and being as fast as Sonic?
The Underground finds a village that has been destroyed by its Freedom Fighter occupants. Why has this happened? It seems to be something to do with the Flybots all over the desert, as Manic finds out when he's injected with a mind-control toxin making him a slave to Dr. Robotnik!
Queen Aleena's Royal Jewel can trace the Queen like a homing device. Having apparently found the jewel, Sonic, Sonia and Manic think they may have found their mother at last. But little do they know it is actually a trap to capture Robotnik; a trap they've just fallen into...
In this episode, the Sonic Underground visit the Oracle again. He sends them to an alternate dimension, where they are the bad guys, and Robotnik is the good guy! They must defeat their corrupted selves and restore peace to Mobotropolis.
While in Robotropolis, Sonic, Sonia, and Manic find an abandoned baby hedgehog. While Sonic and Sonia search for its parents, Manic is left to mind it, and get in touch with his mothering instincts. But the baby isn't as innocent as it looks... and Robotnik comes within an inch of uncovering the sanctuary.
In order to raise money for his own cause, Robotnik auctions off artifacts from the lost city of Mobupinchu. But these artifacts are actually from more recent history; they are bombs, and they're about to go off. When the bomb lands in Bartleby's hands, can Sonic and co. stop Robotnik from finding the real Mobupinchu and save Bartleby?
The Sonic Underground journey through the treacherous Mobian desert as they try to locate a hidden temple filled with prophecies of Robotnik's defeat. But, with Sleet and Dingo in hot pursuit, can the Sonic Underground find the scrolls before it's too late?
The Sonic Underground come across a nomadic tribe whilst journeying through the desert. However, Manic doesn't seem to trust the tribe's leader, "Ifyoucan". He sets off to find out the truth, and uncovers a shocking secret...
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