Plot:
Ax has contracted a disease, an alien virus that is killing him. The only known cure lies in the Yeerk pool. That's right, it's another Yeerk pool mission. Except this time, the only way the Animorphs can get in is to be one of them. Even worse, Jake, Tobias, Rachel and Marco have also come down with Ax's sickness. So Cassie is on her own.

Comments: I and many other Anifans have been waiting for this book for a long time. It's another one of those thought-provoking, bittersweet Cassie books. And yes, it is "The Return of Aftran" . . . kind of. A must-read for #19 fans.