Superhero Mucus Phlegmball is back! Fresh on the heels of his defeat of the radioactive mutant squirrels, Marcus is shocked when his best friend, Chunk, shares his plan to borrow Dr. Boogerslinger's time machine to steal the answers for a math test. Fearing his buddy might flunk fifth grade, Marcus reluctantly agrees, but immediately regrets it when an unexpected power outage throws the boys off course through a wormhole in space.

Instead of going forward a few days to Lugeyville Elementary, the pair soon discover they have landed on a strange sunless planet inhabited by zombies. In a hurry to get home, they don't notice they've picked up a stow-away, a dangerous alien wereduck. Upon landing, the unwanted passenger escapes, tearing up Dr. Boogerslinger's lab and eventually attacking two classmates, putting all of Lugeyville in danger.

The trip through the wormhole also seems to have triggered a new "ability" for Chunk. Every time is he is scared or stressed, his butt takes over and shoots him up in the air. These radioactive rocket farts are combined with an awful stench and a green mist capable of knocking a person out cold. At first, Chunk is worried he might be sick, but when Marcus reminds him he once hit him in the butt with a radioactive snooger, the boys come to the conclusion they are now a superhero duo.

Working together, Mucus Phlegmball and his sidekick, Master Blaster, must save their town by capturing and returning the vicious wereduck to his home planet. Can these two still inexperienced superheroes once again save the day?