Tails builds a seesaw and invites Sonic to play on it when Rotor jumps on in a rush. Tails is thrown into the roof of Freedom Fighter HQ, and when he falls loose a map comes with him, showing the way to "Uncle Chuck's most important treasure." Sally mentions that money is useless, but Sonic reasons that since Chuck was an inventor, it could be something to stop Robotnik, and the Freedom Fighters leave to find it.
They follow the map to Mobius National Park where they find Robotnik has completely polluted it with waste. Two Swatbots overhear the gang talking about the treasure and report to Robotnik. As the waste gets to Sally, Sonic finishes the map at super speed. Just as he finds the X, Dr. Robotnik appears with a group of Badniks and starts to fight. The Freedom Fighters split up, saying it's their best chance at escaping, to which Robotnik says will be more fun.
Sonic saves Tails, Rotor, and Sally from a Burrobot, two Swatbots, and a Buzzbomber. Sonic notices that Robotnik has mysteriously disappeared so they dig up the treasure chest. As they prepare to open it, Sally's words make Sonic realize something and he isn't upset when Robotnik swoops down and steals it. Sonic leads the gang back to Knothole, saying that he doesn't want to be around when Dr. Robotnik opens the chest. In Robotropolis, Robotnik is furious that the chest contains Sonic's bronzed baby shoes, which Uncle Chuck kept because he was sentimental.