“We can’t tell anyone who we are or where we live. It’s too risky, and we have to be extremely careful. We don’t trust anyone, because if we’re discovered… well, we just won’t let them discover us. The main thing you should know is that all of us are in great danger. All of us. Even you.”
This is how the heroes of the book— the Animorphs — think: kids who were given the ability to turn into animals. This is safe, but only under one condition: in an animal form you can’t stay for more than two hours, otherwise you’ll remain in that body forever.