Rachel's got some pretty strange stuff happening. She can't control her morphing. One minute, she's doing homework. The next, she's morphing a full-grown crocodile, and - without returning to human form - she becomes an elephant. That's when the floor gives way and Rachel finds herself looking up at what used to be the kitchen ceiling. What's going on? No one's sure, but Rachel and the other Animorphs have to figure it out - quickly. Because if someone sees Rachel's out-of-control morphing, the other Animorphs are in for some serious trouble.

Tobias has gotten used to his new life. He's a red-tailed hawk with the mind of a kid. It was difficult when he first became trapped in his morph, but he's started to come to terms with things. After all, how many kids actually get the chance to fly? But now Tobias is about to make a very difficult choice: a choice that the other Animorphs know nothing about. And it could mean the difference between living the rest of his life as a hawk...and being human.

There's a new rumor in town. Someone has discovered an item that proves life on other planets exists, and they've been hiding it on a base called Zone 91, the most secret place on Earth. Cassie and the other Animorphs already know about life on other planets. Too well. Their enemies the Yeerks will try to access Zone 91, to find out if what's there will threaten their mission to conquer to the planet. So the Animorphs decide to pay Zone 91 and the Yeerks a little visit. But what they discover is not at all what they expect.

Almost nothing could be as bad as finding out your mother is Visser One, the most powerful leader of the Yeerk invasion of Earth. But it happened to Marco. And even though he's been handling it pretty well, he knew there'd come a time when he'd have to face her again, knowing that the Yeerk in her brain has taken his mother away. So when Marco and the other Animorphs discover that Visser One is overseeing a secret underwater project, they know they have to check it out. But Marco's not sure if this is a battle he'll be able to fight.

Jake's made a pretty amazing discovery. It seems like there may be other people who know about the alien invasion of Earth. Others who know about the Yeerks. Jake finds a website devoted to revealing the existence of the Yeerks, but he and the other Animorphs suspect it might be too good to be true. If they try to investigate the site and it's a trap, the Yeerks could find out who they are. If they don't check it out, they'll never know if they're the only ones fighting.

What's tasty, good for you, and only takes 60 seconds to make? Oatmeal. And because of a strange reaction to the Yeerk's physiology, it's making the would-be invaders of Earth more than a little crazy. Now Rachel and the other Animorphs have a new weapon against the Yeerks. Sounds good, right? Wrong. Because using this advantage against the Yeerks has dire consequences for their human hosts. In order to avoid hurting innocent people, the Animorphs will have to make another trip to the Yeerk pool, where they barely escaped with their lives.

Ax and the Animorphs are about to have a huge problem. It starts when they decide to morph into mosquitoes in order to slip by some unsuspecting Yeerks, and ends with them stuck in Zero-space with no idea how they got there, no way back to Earth...and no oxygen. Luckily, an Andalite scout ship finds them before it's too late. But now Ax is finally with his own people. And he doesn't know if he ever wants to go back to Earth.

There's something pretty weird going on in the woods behind Cassie's house, the place where Ax and Tobias call home. It seems the Yeerks have figured out one very important fact: Andalites cannot survive without a feeding ground. Visser Three knows the "Andalite bandits" don't feed where he does, so there can only be one other place. Now the Animorphs have to figure out a way to stop a bogus logging operation. Because if Visser Three finds Ax in the woods, nothing will stop him from finding the Animorphs.

Cassie's had it. After the last mission, she realizes she's getting tired of missions. Tired of battles. Tired of being an Animorph. She decides that she just can't do it anymore. So she quits. But the war for her planet isn't so easy to quit. It seems a human-Controller named Karen followed Cassie after the last run-in with the Yeerks, and she knows Cassie has the ability to morph. If she exposes Cassie, it's all over. No more Cassie. No more Animorphs. No more planet Earth.

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. But deep inside, Ax knows he isn't their friend. He can't ever be. Andalites must always hold themselves apart, even from their allies. As the Animorphs' past actions start resulting in deaths of innocent people, however, Ax's loyalty is called into question. Now he must decide whether to reveal the reason for his estrangement - the shameful secret of his people.

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. But right as things are looking their most dire, everything stops. Everything. Then Rachel and the Animorphs hear a voice. It belongs to a very old, very powerful being, and it says it can save them. But if it does, the Earth will be defenseless.

It was bad when Jake found out his brother was one of them. A Human-Controller. A slave. But that was nothing compared to this. When the Animorphs decide to visit the Yeerks' 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.

There is a new Animorph. And he's arrived just in time, because the Yeerks are preparing their biggest takeover ever. Their ultimate target: the world's most powerful leaders, all gathered together in one place. What better way to get into the minds of humans? Literally. At first, David joins the fight with a vengeance. But there's definitely something wrong. Because he's starting to break the rules, taking risks that could get them all captured. Or killed. The Animorphs don't know what to do.

Marco never wanted to be an Animorph. He didn't want the ability to change into any animal he touches. And he certainly didn't want to be one of a handful of kids that are the planet's only defense against a secret alien army. His friends know why he feels the way he does. He's worried about his dad - the only family Marco has left. If anything happens to him, his father will be alone. But something big is about to change for Marco. Something that could finally give him a reason to fight. 

David, the newest Animorph, is not what he appears. His need to control the other Animorphs is all he thinks about. And the things he does are starting to break up the group. Rachel and the others know that time is running out. The newest battle against the Yeerks is the most important one yet. And it's not one that will wait. Winning this fight could mean slowing down the invasion. But no one knows what to do with David. Because the newest Animorph is more than just a little problem. He's deadly.