Ax and the rest of the Animorphs have fought side by side for a long while, but there's one thing that can strain a bond between friends, and that's the acquisition of a boyfriend or girlfriend. So when Ax falls for a female Andalite his own age, the strain begins.

Unfortunately, it seems that the Andalites have a darker purpose on Earth, one involving an insidious form of biological warfare. With all that is going on, Ax's loyalty is being questioned big time. And the Animorphs aren't sure whose side he'll take....