Animorphs/The Escape #15, The Warning #16, The Underground #17, The Decision #18, The Departure #19

The Capture: We can't tell you who we are. Or where we live. It's too risky, and we've got to be careful. So we don't trust anymore. Because if they find us.... The Sickness: Something is very wrong with Ax. He's sick. And the Animorphs don't know what do do about it.