With Halloween approaching, Leyton and Wade Tardy are trying to come up with totally awesome costumes. Whoever has the best costume will win the King of Candy Contest. Unfortunately, bossy Fibby Mandible and the awful Barton Slugg have their eyes on that prize as well. As if that wasn't enough, the fiercest, meanest, most sinister aliens in the entire universe suddenly appear in Leyton and Wade's neighborhood. Will the Tardy Boys be able to save the Earth from destruction?