When Charlie receives a dire warning from the Land of the Dead about an impending catastrophe, he travels back in time to 1950s Cuba, where he unravels dark secrets and faces unspeakable evil in a race against time to save the world.

"Mason and Ty were once the very best of friends, like two nerdy sides of the same coin ... until seventh grade, when Ava Petrakis came along. Now Mason can trace everything bad in his life to that terrible fight they had over the new girl. The one thing he'd give anything for is a do-over. But that can't happen in real life--can it? As a science kid, Mason knows do-overs are impossible, so he can't believe it when he wakes up from a freak accident...

So far the AstroNuts have failed to find a suitable planet, but NNASA has come up with a new plan: send the four animal astronauts back through time on Earth where they are to contact early homo sapiens and somehow set them on a path to a sustainable future--trouble is, humans seem inferior to many of the other species (especially the wolves), so the AstroNuts come up with a Survival of the Fittest Olympics, hoping that with a little help the humans...

"The magic tree house whisks Jack and Annie away to South America, where they must climb Machu Picchu to save a baby llama"--

Told in their alternating voices, twelve-year-old neighbors and former best friends Cora Hamed and Quinn McCauley begin working together to open a wormhole so they can travel through time to prevent the school shooting that resulted in the deaths of Cora's sister and Quinn's brother.