Remember when hitting up your school's book fair was the most exciting event of the year? As every former child bookworm knows, there was nothing better than rushing into your school's library and seeing all of the books, just waiting for you to take them home. Every book fair had a couple of hot-ticket books that you knew were going to sell out quickly, and you knew if you had a bad time slot you would never get your hands on them. In my school, those were usually The Animorphs books by K.A. Applegate.

In case you lived under a rock as a child, The Animorphs series takes place in a terrifying dystopia in which humans are enslaved by slug-like creatures that crawl into their ears and take over their bodies. Anyone could be enslaved without realizing it. The only ones who can save humanity are a blue centaur-like alien with no sense of humor and a bunch of kids who can turn into animals for two-hour increments. So... it sounds like Earth is doomed.

Of course, the Earth isn't actually doomed, and despite (or perhaps because) of the dark nature of the books, my friends and I devoured these books as kids. The series had everything: young and compelling protagonists, aliens, people turning into animals, and the occasional preteen romance. Writers, take note: this is the formula for the perfect children's/YA series.

Though the series spanned over 50 books, I've picked out what I believe are the top 10 installments in The Animorphs series. (Spoilers are ahead for anyone reading this after time-traveling directly from 1998.)

This book gave me all the feels when I first read it as a kid. Cassie decides to quit the Animorphs... but then she meets a young girl who's being controlled by the yeerks. Turns out, not all yeerks are complete monsters; they just want to live in a human body rather than live as blind, senseless slugs. So Cassie strikes a deal: she promises to be trapped forever as a caterpillar if the yeerk will set its young host free. Cassie has always been the moral center of the series, and nowhere is it better on display than in this title.

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After a particularly bad battle, Jake is given the chance of a lifetime: to go back and live a life in which he and the other Animorphs never inherited morphing powers and learned about the yeerks. Exhausted, he accepts the offer, and the gang begins living in an alternate timeline in which they have no hand in the battles. Too bad without them the yeerks are left to infest Earth unchecked...

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Rachel is, in my opinion, the most interesting member of the Animorphs crew. A beautiful young girl she finds that she enjoys the human-yeerk war a little more than she should. In fact, her emerging bloodthirsty nature begins to worry all of the Animorphs — including her. When Jake asks her to turn to violence for the good of the cause, Rachel begins to examine the person she's turning into.

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The final battle is here, and we have to say goodbye to at least one of the Animorphs forever (seriously, is anyone else still freaking out about the open-ending?!). Rachel's suicide mission at Jake's command early in the book is tragic, but what's even more heart-wrenching is watching the kids try to adjust to life after the war. After years of being soldiers, they're unable to live as normal humans again and choose to rush back into battle when the opportunity is presented to them. This is one of the darker endings to any of the series I read as a kid.

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The very first book in the series gives the protagonists and readers a rundown on the current alien situation: a bunch of slug-like creatures called yeerks are taking over human bodies, and the only ones that can stop them are a group of kids who were granted the power to shapeshift into animals by a dying alien. What really makes this book one of the best, though, is Tobias's permanent transformation from boy to hawk.

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Tobias has been trapped in his hawk body for several books now, and it honestly doesn't seem all that bad. Better than his crappy home life used to be, at least. But when he does a massive favor for the Ellimist and is granted the power to morph again, he has to decide between staying a hawk who can morph or returning to his human body to live out the rest of his normal life. A choice that's made even harder by his kinda, sorta relationship with Rachel.

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Marco's mother has long been the host of yeerk leader Visser One. The Animorphs thought she was dead, but Marco has discovered that sh, and Visser One are still alive. Now he has to decide whether to continue to hold out hope that she can be saved, or to kill her and Visser One once and for all. While the end of the book leaves us unsure about her fate, we do see Marco decide to kill his mother, which is jarring.

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This one's kind of a strange (duh, you could probably tell from the title), but it gets points for giving us a little information about the mysterious Ellimist. Just as the Animorphs are in danger of being discovered, a powerful creature called the Ellimist transports them away and tells them that their battle is hopeless. He's willing, however, to save them and their families by leaving Earth to the yeerks and taking them to a new planet. What will the Animorphs decide? (Considering there's like a million books after this, probably not to live on new Earth.)

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The Ellimist is back, and he needs the Animorphs help in his deadly game of chess with the Crayak. He asks the Animorphs to act as his champions against the Crayak's army of Howlers as they fight for the fate of the Iskoort race, inhabitants of a far away planet. Jake and the gang want to help the Ellimist, but are they willing to slaughter the Howlers to win the battle? Will they one day be willing to kill millions of yeerks to save humankind? Pretty heavy questions for young teens.

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Our favorite blue alien, Ax, finally gets to narrate his own book in the series in The Alien. Not only do we get to see the human world through alien eyes, but we learn more about the Andalites, Ax's people and the ones who gave the gang their morphing powers. Spoiler alert: they're kind of jerks, and they're not exactly in a hurry to help the human race. At least we have Ax to provide a little alien support.

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