On the night before Halloween, Chris and Meg rescue a kid from a gang of bullies. At first, they think this kid is in costume -- but he turns out to be a bald, pink alien called Weirdo! Weirdo is smelly and gross, and the twins can't get rid of him. But things are about to get even worse. Weirdo has invited hundreds of aliens to town for a full-scale invasion during Halloween! Chris and Meg desperately need a plan... Can the mysterious souvenir they brought home from HorrorLand save them?