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 that Mysterious Monsters are real, they’re making plans of their own. They’ll need clever disguises, well-hidden walkie-talkies – and more than a few broken eggs – to find out, once and for all, what’s hidden in the notorious Area 51.
The Mattigan kids don't believe in things that go bump in the night. After all, their dad is famous for proving such things are impossible. But, when their long-lost Grandpa Joe shows up with his Mysterious Monsters journal, begging for help, the siblings find themselves drawn into a search for Bigfoot.
The Mysterious Monsters hiding in the Mattigan’s basement have discovered they have something in common. When clues about this link point to an island in Canada, one where a werewolf has recently been sighted, Maddie, Max, and Theo convince their dad it’s time for one more mission. The kids are determined to help their friends uncover the truth about their pasts—but also to uncover the truth about their own.
Maddie, Max, and Theo Mattigan know everything now. They’ve solved the mystery of their Monsters’ history, and even of their own. But Happily Ever After doesn’t seem to be how their story was meant to end. There’s an evil creature out there, more mysterious and monstrous than anything they could imagine. And it’s coming for them. This time, the hunters have become the hunted.