Megablast is preparing for a show at the local retirement home. However, the band starts to have creative differences when Alex wants to rock hard while Theo wants to make a sound that's more chill. Their practice gets derailed quickly when they learn that Kaboom has unleashed his new device on Greenville: a machine that's turning everyone into babies. Together, they work to thwart Kaboom's plan while also coming up with a stellar mashed-up new tune.