In a post-cataclysmic world threatened by stinking ooze, a brave girl searches for her missing parents with the help of talking animals and evolving powers. When a mountain spirit challenges her to save the planet, she and a flying frog must overcome a magical, malicious castle of sand and a shapeshifter who wants her dead.

"Mustn't. Just mustn't. Now run along and be a good girl like the others..."

But the protagonist in Waterwight isn't like the others. She's done with being shunned by those who refuse to discuss "The Event," the global catastrophe that changed the planet, left them orphans, and continues to pose a threat to frightened survivors.

Celeste has been troubled by bizarre dreams and nightmares while living in the children's home, and shortly after running away one night in search of answers, she questions her sanity when it appears she can communicate with animals. Delighted in other evolving powers, especially her ability to fly, she nevertheless questions a mysterious mountain spirit's challenge that she must find the key to stopping the water - a silvery-pink, stinking ooze that destroys everything in its path.

But Celeste has no idea how to do it or why she's the one who must find the answer.

She also doesn't know why a wicked shapeshifter wants to kill her.

A flying frog, Orville, saves her from certain death and becomes her guardian as she navigates to a village of superstitious survivors on the other side of the big water. There, she finds other young people with emerging superpowers; they are kept isolated and in fear, though, by one old lady who disciplines the survivors.

Meanwhile, the planet continues to change in horrible ways.

Although Old Man Massive tells her she must hide her true identity, he also reminds her to "never forget who you are." Celeste must discover who she is to save the planet.