Professor Maximilian Mousemover just arrived in Muskrat City in a time machine. Tony Sludge's great-great grandfather Butch Sludge is visiting from the past, too, and he's up to no good. The Heromice must travel through time to save the rodents of the past-- and the future-- from the Sewer Rats.

Original title: Superger e la supermacchina del tempo.