Dash posted info about the plot on the official TSS website yesterday:
Yes, it does use the Sonic Adventure settings, but it’s a little different. Anyway, Sonic and his friends, Tails, Amy, and a new, mysterious character that goes by the name Sal (yes, it’s Sally Acorn, but Sonic doesn’t know that), will search for seven chaos emeralds. Each emerald they find will enable a secret power! For example, if Sonic found the Fire Emerald, he would receive the Fire Spin Dash (A move, duh). Sort of like a RPG, eh? And I told you this comic is A LOT like a RPG, and here’s proof.