After Sentinel Prime and his forces have conquered the Earth, they relocated the planet's human population -- all except for a girl named Barbara Gordon AKA Batgirl, who's managed to hide from the aliens. When Barbara meets a fugitive blue hedgehog named Sonic, there's mutual distrust. However, Sonic is not like others; he craves friendship and fun. As their distrust fades, the pair set out together to find her father Jim Gordon and her best friend Harleen Quinzel (who is secretly Harley Quinn), but, unbeknown to them, the Quintessons -- Sentinel Prime's masters (who no one knows about)-- are en route.