The class dig up a mysterious time capsule which sets them off on a race to find hidden treasure before Walter or a greed-crazed Paul the Potato can find it first.

Power-hungry tiny alien Empress Miasma takes control of Gnasher from the inside and uses him in her attempts to take over planet Earth. But when Miasma breaks out of Gnasher into Beanotown for real and Walter helps her grow in size, mayhem really takes hold!