With Bigfoot safely stashed in their basement, Maddie, Max, and Theo Mattigan are off to Las Vegas with their dad. His plan is to prove there are no aliens on the loose there. 

But now that his kids know Mysterious Monsters are real, they're making plans of their own. They'll need clever disguises, a well-hidden walkie-talkie — and more than a few broken eggs — to find out once and for all what's hidden in the notorious Area 51.