The Earth is being invaded, but no one knows about it. When Jake, Rachel, Tobias, Cassie, and Marco stumble upon a downed alien spaceship and its dying pilot, they're given an incredible power—they can transform into any animal they touch. With it, they become Animorphs, the unlikely champions in a secret war for the planet. And the enemies they're fighting could be anyone, even the people closest to them.
If someone told you Earth was under a secret invasion, what would you think? Rachel had a hard time believing it, even after she and her friends saw what they saw—and received an incredible power to become any animal they touch. Rachel knew they were in danger from the start, so when it's suggested that they use their new powers to spy on one of their enemies, she rises to the challenge.
When Tobias and his friends were given the power to morph, they were also given an important warning: Never stay in a morph for more than two hours. But Tobias broke the time limit, and now he's trapped in the body of a hawk—forever. Tobias won't give up, though. So when he discovers an important Yeerk secret, he knows he has to do everything in his power to destroy it.
It all started with the dreams, but Cassie didn't pay much attention to them. She and her friends have been having nightmares ever since they acquired their power to morph. But when Cassie discovers that Tobias has been having dreams too—the exact same dreams— and a voice that's calling to them for help, she decides it's time to start listening.
Marco never wanted to be an Animorph. He certainly did not want to be one of a handful of kids who are the planet's only defense against a secret alien army. He's worried about his dad—the only family Marco has left. If anything happens to him, his father will be alone. But something is about to change for Marco, something that could finally give him a reason to fight.
When the Animorphs decide to visit the Yeerk's new base, it seems simple. But then they get caught and Jake falls—just for a moment—into the Yeerk pool. Now they're out, and his friends can't see it. To them he's just like normal. But Jake is screaming for help. His worst fear has finally come true. He's become the enemy.
The last time Rachel and her friends entered the giant Yeerk pool beneath their town, things went very bad. This time, they plan to be careful, and sneak in as roaches, just to spy. Once they’re inside, though, the team gets caught. Then Rachel and the Animorphs hear a voice and it says it can save them. But if it does, the Earth will be defenseless.
Ax is an Andalite, an alien, stranded on a strange planet he's sworn to defend, even though it's not his own. Since the Animorphs rescued him, he's fought at their side, and in that time they've come to consider Ax a friend.