M y name is Cassie.

I can't tell you my last name. I wish I could. But I can't even tell you what town I live in or what state. We have to disguise our identities, we Animorphs. It's not about being shy. It's about staying alive.

If the Yeerks ever learn who we are, we'll be done for. If they don't kill us outright, they'll make us Controllers. They'll force a Yeerk slug into our brains, where it will take control of us, making us slaves - tools of the Yeerk invasion of Earth.

And I really don't like the idea of being under the control of an alien. I don't like the idea of being dead, either.

On the other hand, there are some things I do like about being an Animorph. Some very cool things.

Take the other night. It was late. I should have been in bed. Instead I was in the barn, get ting ready to turn into a squirrel.

Technically, the barn is really the Wildlife Re habilitation Clinic. My dad is a vet. So is my mom, but she works at The Gardens, this big zoo. The Wildlife Rehabilitation Clinic is just my dad and me. We take in injured birds and animals and try to save them, and then release them back into their natural habitats.

That's where I was. In the barn. Surrounded by dozens of cages full of birds, from a mourning dove that'd run into a car windshield to a golden eagle that'd almost been electrocuted by a power line.

In another part of the barn we have bigger cages for the badgers and opossums and skunks and deer and even a pair of wolves who'd been poisoned. At the other end (far from the wolves) we keep our own horses.

There's an operating room and a couple of small recovery rooms, too. That was a new thing. My mom and dad recently got a big donation from a rich family in Ireland. They were finally able to refurbish the antelope exhibit in our family theme park, The Gardens, and we still had plenty to spare for new medical equipment. I just felt dirty accepting money from the Fowls.

Back to that night. Have you ever watched a squirrel in the park? They are constantly alert. Constantly looking around. It's like every minute of every day they're thinking, "Hey! What's that?"

So I knew that if I morphed into a squirrel, all that nervousness and fear would become a part of me. It's something we've all had to deal with: controlling the animal instincts, the animal mind that comes along with the animal body.

Anyway, that's where I was, in a gloomy barn with just the yellow overhead bulbs to light the room. Why was I there? Because someone, or something, had been sneaking in and getting at the birds. We'd lost a patient just the night before. A duck.

I couldn't sleep, anyway. I kept having these dreams. Only they weren't like normal dreams, somehow. More like ... I don't know. Just really strange, that's all.

"Relax, Magilla," I whispered to the squirrel in my hands. "This won't hurt at all." I pulled some chestnuts from my pocket and handed him one. Another nut fell to the floor.

Some morphs are easy. Some are terrifying. When I was a horse that was cool. When I had to become a trout, well, that was a little weirder. The whole time I just kept thinking how someone could fry me and serve me with tartar sauce.

And I don't like tartar sauce.

"Squirrel," I told myself. I always try to get into the feeling of what it might be like to be the animal before I even start morphing.

The first physical change was in my size. I started shrinking. It's a very bizarre feeling. See, you feel like you're standing totally still, but the ground keeps coming up toward you. And the ceiling is moving away. Door handles aren't where they should be anymore. All of a sudden they're over your head.

I had shrunk to maybe two, two-and-a-half feet tall when my arms came sucking back into my body. Right about that point, the real Magilla tore out of there. He ran back to his cage, got in, and - I swear this is true - closed the door. Anyway, I still had normal (although short) legs, but my arms were stunted. I still had the normal number of fingers, but they were teeny tiny now, way too small for my body.

My ears traveled up the side of my head to rest on top. Soft gray fur spread across my body in a wave. My face puffed out and grew pointed.

Then, the wildest thing! My tail sprouted out of my body! And what was cool was that I wasn't a squirrel yet. I was still about half human, the size of a small child, and my tail just shot out, about two feet long! Much longer and bigger than it would be once I was totally squirrelified.

I tilted my head back and I could see this bushy gray tail arched up over me. Way cool. My legs sucked in and I was down on the ground, down on the cement floor of the barn.

I suddenly discovered I hadn't swept and mopped as well as I thought I had. Amazing what you can see when your face is just an inch from the floor.

Then the squirrel brain kicked in.

WHOA! YOW!

Man, did I have energy!

It was like I was plugged into a million volts. I was supercharged! My slow, sluggish human brain was just blown away by the sudden explosion of energy.

A noise! What's that? I cocked my ears. I swung my head, focusing my big eyes. A bird in a cage!

A new sound! What was it? I spun around. No, wait! What was that? And that? And what was the other sound? PREDATORS! They were everywhere! I was surrounded! PREDATORS!