As far as classic plots go, Fantastic Beasts and Where to Find Them…doesn't really have one.
Nope. It's actually written in the style of a parody encyclopedia. (Which, we know: "parody" and "encyclopedia" sound like they'd go together about as well as "peanut butter" and "Hawaiian pizza." But remember: this is from the same author who made "fluffy pink cardigans " synonymous with "totally evil.")
Basically, the idea is that this guy—Newt Scamander—has travelled around the entire world hunting down all kinds of magical creatures. He's studied them and documented his experiences with them and written it all down in this book. Fantastic Beasts and Where to Find Them is the guide to every known creature in the wizarding world. There are seventy-five, but more new species are being discovered every day.
The guide starts with a little bit of backstory on Newt Scamander. He was interested in fantastic beasts as a boy and, after graduating from Hogwarts School of Witchcraft and Wizardry (ever heard of it?), he went to work for the Ministry of Magic in the Care of Magical Creatures Department.
In 1918, a publishing company offered him the chance to earn a few extra Galleons travelling the world compiling a compendium of magical creatures. The book is now in its 52nd edition, so the rest is pretty much history. Magical history, that is.
Before getting into the beasts themselves, Mr. Scamander offers a little history of how creatures came to get labeled as beasts. Centuries ago, wizards had to figure out which magical creatures could be called "beings" and which could be called "beasts." If you were a being, you got to be part of the magical government and have legal rights. If you were a beast, well, you didn't.
So, it's complicated. But basically, in 1811, what everyone ends up coming up with is that if a creature could understand the laws of the magical community and help create and uphold those laws, then they got to be classified as beings. Everyone else was a beast. Except for ghosts, who were spirits. And centaurs and merpeople who were technically beings…but asked to be beasts because they didn't want to be bothered with all this magical nonsense.
Mr. Scamander also gives us a brief overview of exactly what Muggles know about fantastic beasts. Some—like dragons, griffins, centaurs, and unicorns—they know about. Or used to know about. Some were never on their radar. But, in 1692, it became necessary for all magical beings and beasts to go underground.
Let's just say the Muggles were getting a little panicky…and when Muggles get panicky they tend to start burning people at the stake.
The remainder of the book is an A to Z guide of all the beasts in the wizarding world with descriptions and illustrations where available. Mr. Scamander covers all the magical creatures from Acromantula right down to Yeti.
And more are being discovered every day. Oh, thanks Mr. Scamander: we really needed to know that that rustling we hear coming from our closet late every night could actually be some six-armed, sharp-fanged, bug-eyes beastie.