<Do not do that,> says the alien, in the sort of tone that leaves no room for argument. <The Yeerks will have infiltrated your emergency services.>
His stalk eyes scan the sky continually while he sweeps his main eyes' glittering gaze across the group.
<There isn't much time. I will have to be brief.>
And then—a whole story flashes into their heads, almost all at once, images and concepts streaming past so quickly that it feels more like remembering a movie you've already seen and know the plot of by heart than listening to someone tell a story.
It begins on a faraway planet, where strange creatures roam over barren muddy ground under a crackling green sky. A lopsided blue ape—Gedd—crouches next to a pool of murky grey water. A slug—Yeerk—emerges from the water and crawls into the Gedd's ear. The Gedd waits patiently for the Yeerk to wrap around its brain, then the combined entity of host and symbiote strides away from the pool, moving more purposefully, squinting at its surroundings with a new alertness in its dull eyes. Together they have the intelligence of the Yeerk, and the senses and mobility and tool-manipulation capacity of the Gedd. They separate every few days so the Yeerk can swim in waters irradiated by the rays of Kandrona, their sun, absorbing nutrients the Gedd's brain can't provide. This is a Yeerk in its ancestral environment. This is how they lived, before—
A spaceship lands.
Blue centaur aliens—Andalites—emerge from the ship and look around curiously. One—Seerow—is particularly fascinated by the Gedds and their Yeerk passengers. He spends hours, days, weeks, talking with them, teaching them, learning from them. He wants to show them the stars.
The other Andalites are more hesitant, worried about the consequences of handing out spaceflight to a society of brain-infesting slug people. They caution Seerow to slow down. There are arguments.
Then the Yeerks attack. They kill several Andalites and steal a spaceship. They have a portable Kandrona, built with Seerow's help; they're not tied to their home planet anymore. They can go where they want, take what they want.
The Andalites are furious. A law is passed. Seerow's Kindness. No Andalite may ever, ever share advanced technology with a non-Andalite again. They must never repeat their mistake.
Meanwhile, the Yeerk Empire grows. The Andalites fight them, but interstellar war is not common and neither side has much practice. Mistakes are made. The Yeerks establish a foothold in the galaxy. They find other inhabited planets and enslave entire species. Taxxons—soft worms with lightning reflexes and eternal ravenous hunger, whose leaders signed away their entire species to the Yeerks in exchange for a promise that Taxxon hosts would be fed in more abundance than their home planet could offer. Hork-Bajir—a simple, peaceful people, whose strong bodies and blade-studded limbs are built for climbing the magnificent trees of their homeworld and cutting bark to eat; the Yeerks took them by force, and now use them as shock troops.
And now, humans.
The Yeerks are trying a different approach, here on this planet with its billions of potential hosts not united by any central authority. Slow infiltration, taking hosts by stealth, avoiding widespread attention so that by the time anyone not under their control realizes they're here it will be too late to fight back. Coaxing some people to be voluntary hosts, taking others by force for their strategic value or as an information security measure or just because it's convenient.
The Andalites fought a battle for Earth, just now. This one—Alvandar—was part of it. They lost. (An image of a great ship, flickering in and out of visibility and trailing smoke as it plunges through the atmosphere toward the ocean.) More Andalites might be coming, or they might not. They might abandon Earth to the Yeerks.
Alvandar does not want to abandon Earth to the Yeerks.
There is a technology. Created originally for scientific and entertainment purposes, to allow Andalites to experience the concrete perspective of other beings, fly through the sky as birds or even transform themselves into members of alien species. A shining blue cube, each side palm-sized—Escafil Device—grants the power to morph.
<I have an Escafil Device in my ship,> he sends. <They'll have trouble putting me on trial for my Kindness after I bleed to death. If you want to help me—take it. Bring it out here. I'll give you morph. It's not much, but on a planet with this level of biodiversity, I think it'll be more powerful than the Yeerks expect. Find them. Spy on them. Disrupt their operations. I'm sorry to lay this responsibility on a handful of children, but there's no time.>