by K.A. Applegate

The Animorphs series is the series about the early adolescents Jake, Marco, Rachel, Cassie, and Tobias, who are fighting against the aliens called "Yeerk". These are the parasitic snail-like creatures. They live inside human body, in the brain to exact, and then take over the central of control system for the whole body, hence a human who has a Yeerk inside his/her brain is called Controller.
There are many planets Yeerks have conquered, and their next target is... the Earth..!

The kids never have a dream to become an Animorph, but coincidentally they met a dying alien, Andalite creature named Elfangor, who then gave them the power to morph into any animal they touch, so that they can continue to struggle against the Yeerk villains that attacking the Earth.

Ever since that moment their life as a kid have changed altogether. Not only the matters of school and a pile of homework they have to face, but also a mission to save the world from Yeerks' conguest.

The morph power is an Andalite's technology. So, the Yeerks think that their enemy is the Andalite army. No one knows that actually they are only a bunch of innocent kids. Animorphs are moving stealthily, in secretive way. No one knows that they have the power to morph, no one suspects that they are fighting against the cruel aliens, even their parents. In school, they pretend as if they don't know too close each other. They must be cautious if they want to meet, or just talking by phone. Also, they can't asking for help to anyone, and believing anyone, because anyone they believe could be a Controller...

Two hours is the maximum limit for them to morph. More that that, they will be trapped inside that animal body, forever....

Those are what make the Animorphs series become a wonderful and nice books to read. As the early adolescents, sometimes the Animorphs behave so rilex and full of jokes in facing their adventures, while truthfully they are very strain and scare. With their morph power, and ally with Ax — Elfangor's little brother —, and a number of aliens who are opposite to Yeerks, they are fighting and fighting again, for annihilating Yeerks.