Fragments from the shattered moon are raining down on Ape City, burning anything that isn't made of stone. Cornelius, son of the Shoemaker, helps a female Chimp, Cassia, who wants to go home to her child and sister to make sure they are safe. Zaius' pregnant daughter needs help and Prisca offers--but she wants an Orangutan doctor, not a Chimpanzee one, which emphasizes the rigid class system. And Chief Burrus, a gorilla, will not let the mass of chimps cross over the bridge to a safer part of the city. Then, the water in the river below vanishes--only to create a flood that covers the city. And as you know, Apes can't swim (denser body mass than humans).
This continues to be an interesting tale and gives an interesting backstory to familiar characters.