Marco is determined to save his father from the Yeerks.

The blue box Elfangor used to create the Animorphs has been found by David, but David doesn't know what it is. The Animorphs have to get that box at any cost. David ends up on the run with the Animorphs and Ax, and may become the sixth Animorph.

Illustrations and simple, rhyming text remind the reader that any achievement may be preceded by mistakes, and learning from them makes accomplishments sweeter.

Endowed by a dying alien with the power to morph into any animal they touch, friends Jake, Rachel, Cassie, Tobias, and Marco investigate the wonders of the world with their unusual powers.

When Marco runs into his old friend Erek he doesn't think too much of it. He's got more important things to do, like helping to save the world. But then Marco finds out Erek's been hanging with some of the kids at the Sharing, and he starts to think that something just a little weird is going on.So Marco, Jake, and Ax decide to morph and check old Erek out. Just to see if he's been infested with a Yeerk. The good news is that Erek's not a human-Controller....

The Animorphs have to make the most important decision they've ever faced: Do they continue to fight the Yeerks in secret, or is it time to let everyone know there's a resistance? That the Animorphs exist and Earth does stand a small chance against the invasion. Jake knows that either choice is a major one, not something that a kid should be responsible for. But he's getting tired of the pressure. Even though he realizes his friends need him to...

Marco's mom is back. But she's not Visser One anymore. Marco's not even sure if she's still a Controller, but he's determined to find out. No matter what it takes. No matter what might happen. Marco wants his mom back. Jake and the other Animorphs realize that Marco is under some serious stress. And that the situation with his mom could very well jeopardize everything they've worked for. Now they also have to wonder if Marco will be the one to give...

What would you do if you were the only alien trapped on a strange planet? Probably freak out, right? Well, that's what Ax feels like doing. But as an Andalite warrior-cadet, he has to be pretty cool about stuff like that. He's been hanging out with the Animorphs ever since the Dome ship was destroyed by the Yeerks and his brother, Prince Elfangor, was destroyed by Visser Three. Life on Earth is pretty different for Ax. But there is one thing he,...

Something is very wrong with Ax. He's sick, and the Animorphs don't know what to do about it. They can't take him to the hospital. They don't know how to contact the Andalite home world. And Ax is dying. Cassie and the other Animorphs come up with a plan. But it involves finding a new way into the Yeerk pool. There's just one problem: Jake, Rachel, Tobias, and Marco all come down with Ax's sickness. And now, for the first time, Cassie is on her...

Sometimes your worst problems are the ones you can't actually see. Like the Helmacrons. These less-than-an-inch-high aliens are back, and they want the morphing cube more than ever. Obviously Rachel and the other Animorphs can't let them take the cube. But when Rachel tries to stop the Helmacrons from stealing it, Marco gets in the way and ends up with tiny aliens, well, up his nose. Rachel and the others can't let the Helmacrons stay inside Marco's...