Noah and his friends in the Secret Society join forces with four teens known as the Descenders to try to protect the Secret Zoo hidden below the Clarksville City Zoo from monstrous sasquatches and the evil Shadow Master.

A little boy visits the zoo with his family for the first time and marvels at all of the wonders it offers.

The animals at the zoo have some unusual requests for a little girl who goes to visit.

"Someone has been sleeping on Elephant's haystack, drinking from Lion's bowl, going potty in Ostrich's sandbox, and scratching Giraffe's favorite tree. Who could it be?"--

For once, operations at the enormous zoo/theme park appear to be running smoothly (except for the occasional herring-related mishap in the penguin exhibit) and Teddy Fitzroy is finally able to give detective work a rest. But then a local lion is accused of killing a famous dog--and the dog's owner, an inflammatory radio host, goes on a crusade to have the cat declared a nuisance so it can be hunted. However, there's evidence that the lion might have...

Orville is a little penguin who lives in a zoo and dreams of big adventures, like going to the Moon; the other animals are skeptical, but Orville is determined, so he builds a spaceship and sets out all by himself--and discovers that real adventures are best when they are shared with friends.