Mystery, Inc. with its newest members head to Riverdale, Wisconsin for an upcoming Rock festival, similar to Woodstock. Shaggy is glad because he gets to see his favorite all-girl rock band, Josie and the Pussycats, perform. As it turns out, the others are also looking forward to seeing them, and they all have back-stage passes courtesy of the band's manager, Alexander Cabot III. It has not been that long since Fred, Daphne, Velma, Shaggy, and Scooby met the Pussycats. It has only been a year, and they have remained in touch since then. Mystery, Inc. is also keen to introduce its newest members. When the mystery solvers finaly arrive, Josie, Valerie, and Melody are glad to see them. So are Alan and Alexander. Alexandra, however, has some problems. While the Pussycats perform, Scrappy-Doo prevents Alexandra from sabotaging their performance and a fight breaks out just as a were-cat attacks the rock festival. They call it the Purple Pussycat. And this monster is after the band. Fred decides they should find clues as to what has happened to which Scooby-Dum takes out a magnifying glass and examines Alexandra because she seems the obvious suspect, almost getting into a fight with her as a result. The others figure that someone else is behind the attack given that Alexandra had gotten into a fight with Scrappy-Doo just before the attack. Could it be Josie's ex-boyfriend, Albert Thomas, who is still bitter about their break-up? Or could it be someone else? They will have to find out.
Riverdale is the main setting of the Archie Comics universe.
This is the first episode to incorporate an episode of The New Scooby-Doo Movies into the rebooted continuity that started with Scooby-Doo! Mystery Incorporated and continues with this series. Previously, Scooby-Doo! Mystery Incorporated only incorporated episodes of Scooby-Doo! Where Are You? in the rebooted continuity it started.