The Return is the forty-eighth book in the Animorphs series, written by K.A. Applegate. It is known to have been ghostwritten by Kimberly Morris. Due to an editorial oversight, Lisa Harkrader was mistakenly credited with writing the book. It is narrated by Rachel and is the first of the last seven books to have an inverted title, in which the main title is in color and the background of the title is in black, showing a definite change.
David, the "sixth Animorph," is back. When the Animorphs and Ax decided to give another human being the power to morph, it was one their biggest mistakes. David tried to destroy all of them - and almost succeeded. Rachel and the others thought they'd seen the last of him when they trapped David as a nothlit. Leaving him on a deserted island to live out his days as a rat...
They were wrong.
Rachel knows what a threat David is. He's cunning and dangerous. Worst of all, he knows their secrets. Now he's captured Rachel as part of his plan to take over everything. David wants power. Money. But more than anything, he wants revenge...
With the help of Crayak, David, the boy who went insane after being recruited to the team, returns for revenge on Rachel after she trapped him in rat form. Ultimately failing, David finds himself in Rachel's clutches again and he begs her to kill him. Whether she did so or not is never revealed in the series.
Rachel "morphs" into several creatures that do not exist except in the world manipulated by Crayak and Drode, including a giant, ambulatory venus flytrap, and a gigantic version of herself with "mechanical claws" and superhuman strength- a possible reference to the Howlers.
At the end of the book, David is seen with Rachel, the former requesting the latter to kill him off, and to end his misery as a rat. Rachel is in a dilemma, for she feels that killing him would be nothing but murder, since he is still part human. The book ends without revealing her decision.