"Round Up!": Wait until you see who just got engaged! But don't celebrate just yet... there's trouble afoot, and now the engagement party has become a seek and capture party for the Freedom Fighters! Along the way, old foes will return, fractured friendship will be restored, and both new alliances... and new rivalries will form! All this, plus a virtual "who's who" of characters from Sonic's epic mythology!
Meanwhile, Sally Acorn is talking to Knuckles the Echidna via a computer transmitter. He informs them that Mina Mongoose's world tour has started off fine. He also tells them that Vector the Crocodile got wind of something important. Rouge the Bat had stolen the Master Emerald and was selling it to the highest bidder. Rotor Walrus says it doesn't make any sense since Rouge has only ever wanted it for herself. Sally says that that is regardless as they must secure the Master Emerald no matter what, especially with so many dangerous forces at large. Knuckles says that he'll return to Knothole as soon as possible to take care of Rouge, but Sally says that the Freedom Fighters owe him this and she volunteers herself, Sonic, Bunnie, and Antoine to take care of the mission.
Later that night, the Freedom Fighters are stationed in the marshlands where the auction is taking place. Soon, Nack the Weasel, Bark the Polar Bear, and Bean the Dynamite arrive, Bean and Bark riding hoverboards. The Freedom Fighters take care of them easily and then go after Rouge. Rouge is awaiting bidders for the "emerald" and believes no one is going to show up, but then Mammoth Mogul and Ixis Naugus arrive to steal the Master Emerald.
Mogul reveals that he was set free by "Anonymous" while in the Egg Grapes in return for his Chaos Emerald, but the experience had left him de-powered and Naugus no more than animal. Mogul attempts to grab the emerald, only for Sonic and Bunnie to stop him. Mogul sends Naugus to defeat them using his new shadow-melding abilities, but he is easily knocked out by Bunnie. Mogul then confronts them himself using his Ixis Magicks, but he is knocked out by Princess Sally on Nack's Hoverbike.
They then attempt to arrest Rouge, but she then reveals that she didn't steal the Master Emerald and that it was all just part of a sting operation she did to show Knuckles she can be a good girl that plays by the rules, using a table, a blanket, and a green lantern. They then place all the criminals on Nack's Marvelous Queen and set off back to Knothole.
Meanwhile, Snively reports into Dr. Eggman that Bean, Bark and Nack have not reported in and that they may have been captured. Eggman then reveals that he knew it must have been a trap, but hired the three Mercenaries to be sure. Snively then tells him that the Egg Fleet has been finished ahead of schedule, and that his other project will be finished right on time.