The book is known to have been ghostwritten by Erica Bobone.
While using their aquatic morphs to chase the Yeerks' new Sea Blade, which was after the Pemalite ship, the Animorphs and Ax find themselves beached inside an underwater cavern. The cavern seems to be littered, however, with several different types of air and sea craft, with what appears to be human statues inside. Further inspection by Cassie and Ax reveals that these people were real, and were killed and stuffed for preservation. While attempting to escape and locate Visser Three, whose ship was taken by a strange, humanoid aquatic species, Jake, Cassie, Ax, Rachel, and Marco, all in their natural forms, are captured by these life-forms, who reveal themselves as Nartec. (Tobias was on lookout above, and therefore was not captured.) The Nartec queen explains that they once were humans who lived above water, and when their city sunk, they began to adapt to underwater life. Ax realizes that radioactivity is what aided their ability to evolve so quickly. He also surmises that the Nartec have inbred for years, except for possible breeding with their captives prior to killing them, so their genetic code is breaking down. After the Nartec queen makes it clear that she intends to "preserve" the Animorphs, she permits them to do some sightseeing, but warns them not to try and escape.
Of course, the Animorphs have no interest in being killed, stuffed, and added to a collection, so they plan to locate Tobias, figure out where Visser Three is hiding, and capture the Sea Blade to escape. However, their plans are foiled by a Nartec ambush from the water, and the Animorphs are taken to an operating room of sorts to be "preserved." Given a mind-numbing agent, Jake begins to slip away, when he notices a Nartec suddenly attacking the other Nartecs in the room and wiping them out. The rogue Nartec demorphs into a Red-Tailed Hawk, Tobias, and aids the others in escaping. The Animorphs climb on board the Sea Blade, only to be challenged by hordes of Nartec, wielding weapons ranging from spears and clubs, to automatic rifles and machine guns. While the Animorphs, in their standard combat morphs, had no difficulty attacking the Nartec and holding them at bay for a while, they began to be worn down by sheer force of number. Finally they struck a reluctant alliance with Visser Three (who had been hiding on the ship the whole time while his crew were killed and stuffed), who guided them in starting the Sea Blade and escaping. Under Jake's orders, Marco, whose gorilla morph was gutted by a sword, opened the hatch to the Sea Blade, and the Animorphs swam to the surface. Visser Three survived as well, though separated from the Animorphs.
Animorphs is an English language science fiction series of young adult books written by K. A. Applegate and published by Scholastic. It is told in first person, with all 6 main characters taking turns narrating the books through their own perspectives. Horror, war, dehumanization, sanity, morality, innocence, leadership, freedom, and growing up are the core motifs of the series.
The story revolves around five humans, Jake, Marco, Cassie, Rachel, and Tobias, and one alien, Aximili-Esgarrouth-Isthill (nicknamed Ax), who obtain the ability to morph into any animal they touch. Naming themselves "Animorphs" (a portmanteau of "animal morphers") they use their ability to battle a secret alien infiltration of Earth by a race called the Yeerks. The Yeerks are a parasitic race of aliens resembling large slugs that take humans as a host by entering and merging with their brain through the ear canal. The Animorphs fight as a guerilla force against the Yeerks, led by Visser Three, and their program to take over the human race. Morphing into animals allows them to battle the various armies of aliens that the Yeerks use, but it also protects their identities. As far as the Yeerks know, only Andalites like Ax have the ability to morph, and if they knew that the Animorphs were mostly human they would be able to easily find out who they are. Protecting their identities becomes more and more difficult as the series goes on because though someone with the ability to morph can change into any animal that they touch, they can only stay in a morph for two hours or they will permanently become that animal. Throughout the series, we see how the war affects the characters in different ways, mentally and physically.