After the events of Monsters vs. Aliens, Susan Murphy (a.k.a Ginormica) and the Monsters are now working with the US government on Special Operations. So, when an alien presence is detected in Susan's hometown of Modesto, California before Halloween the team are dispatched to investigate. Everything appears to be normal, right down to the pumpkins peering out from every doorstep and windowsill. Yet when Halloween arrives, these innocent-looking carved pumpkins reveal themselves for what they really are – mutant aliens. The altered pumpkins then start to implement their fiendish plan to take over the Earth. The Monsters are there to try and combat the mutants and smash their wicked scheme!