CONTROLLERS. There's a word you need to know. A Controller is anyone with a Yeerk in his head. Yeerks are alien parasites. They are evil little slugs who live in the bodies of other species and enslave them. All the Hork-Bajir are Controllers. So are the Taxxons. So are more and more humans. Human-Controllers...

Out they leaped, one after another. Seven feet tall. The most dangerous-looking creatures you'll ever want to see. Foot-long, razor-sharp blades raked forward from their snake heads. More blades at their elbows, wrists, and knees. Feet like Tyrannosaurus rex. The shock troops of the Yeerks. HORK-BAJIR warriors...

The TAXXONS are the second most common type of Controller. Imagine a very big centipede. Now imagine it even bigger, twice as long as a man. So big around, you couldn't get your arms around it...Taxxons are gross, disgusting creatures. Unlike the Hork-Bajir, who were enslaved against their will, Taxxons chose to turn their minds over to the Yeerk parasites. The are allies of the Yeerks. I don't know why...

And last, he stepped out: dainty Andalite hooves. Deadly Andalite tail, like a scorpion's. The mouthless Andalite face. The two small Andalite arms with too many fingers. The two mobile eyes mounted on antlerlike stalks that turned this way and that, always searching, so that the large main eyes could focus on one thing at a time. An Andalite body. But not an Andalite mind. For in that Andalite body lived a Yeerk...The only Yeerk to have the power to morph...VISSER THREE...

THE YEERK SHIP was huge...Compared to this thing, the biggest jumbo jet ever built was a toy. It was shaped like a manta ray. There was a bulging, fat portion in the middle, with swooped, curvy wings, one either side. On top of the wings were huge scoops, like air intakes on a fighter jet, but much bigger. You could suck a fleet of buses in through those scoops. The only windows were in a small bulge at the top. The bridge, I realized...