Something is very wrong with Ax. He's sick. And the Animorphs don't know what to do about it. They can't take him to the hospital. They don't know how to contact the Andalite home world. And Ax is dying.

Cassie and the other Animorphs come up with a plan. But it involves finding a new way into the Yeerk pool. There's just one problem: Jake, Rachel, Tobias, and Marco come down with Ax's sickness. And now, for the first time, Cassie is on her own...


Released: April 1999
Pages: 152
Cover Art by David B. Mattingly

Front Cover (Hi-Res)
Inside Cover (Hi-Res)



Inside Cover UK Cover
U.S. Inside Cover
U.K. Cover German Cover French Cover


  • ANIBASE: The cover of this book was one of the few regular series titles to feature an alien morph. For all the other books, cover artist David B. Mattingly used photographs of the character models and the animals, and then "digitally painted" them in Photoshop. But for these alien morphs, he went back to his pre-computer roots and painted the aliens by hand. The only alien that wasn't completely fabricated was Ax himself -- a model was actually hired to make poses, and David Mattingly painted over him!
  • Aftran makes her return here from #19: The Departure. The promise she made to Cassie to never take another host involuntarily has apparently been noticed by other Yeerks, bringing her directly in Visser Three's line of sight for torture, to find out more information about the new Yeerk Peace Movement that has noticeably begun to spurr amongst the Yeerks.
  • This book marks the first time where a Yeerk (Aftran) receives the power to morph in their natural state. Aftran uses the morphing ability to turn into a humpback whale nothlit, promising never to go back as a Yeerk. Not only does this provide a peaceful solution for Aftran's search for freedom, but (unknown to the Animorphs, and the fans at the time) it forshadowed the importance of the Escafil Device and the events that were to come later in the series in the ending of the war.



ANIBASE: New to the series are Mr. Tidwell, a teacher at the Animorphs school, and the Yeerk in his head, Illim. Mr. Tidwell is a voluntary host to Illim, since Illim is part of the Yeerk Peace Movement. Together they work to help bring down the tyranny of Yeerk slavery from the inside. They are the ones who alert Cassie to Aftran's plight, and it is Illim that Casie ultimately ends up morphing.


Jake Eel.
Rachel Eel.
Cassie Eel, and Yeerk (Illim)
Marco Eel.
Tobias None.
Ax None.
Aftran Humpback Whale.
Visser Three Unnamed Creature



Tria Gland
A gland in the back of an Andalite's head that keeps disease-carrying organisms away from the rest of the body.

A sickness that results when disease-carrying organisms overwhelm an Andalite's Tria Gland, causing it to inflame and eventually burst. Turns out that yamphut is contagious, and soon everyone except for Cassie is infected with the Earth version -- the flu.

Yeerk Peace Movement
Started by the simple alliance between Cassie and Aftran, the Yeerk Peace Movement is made up of Yeerks who oppose their leaders' choice to enslave innocent creatures. These Yeerks would rather find another way to gain the eyesight and the other senses that they, as parasites, crave.



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