In a world very much like ours (but with magic), children are given the Nectar on their eleventh birthday. A small number of them will summon a Spirit Animal. 
 That's the basic plot behind the Spirit Animals series, which is authored by several popular fantasy/sci-fi authors. And the first one -- "Wild Born" by Brandon Mull -- is mostly about introducing the characters, the world, and some nebulous villains who have plans to do... something. Neither the characters or the plot are very well-defined yet, but it's a passable introduction to Erdas. 
 Four different children from four different countries are given the Nectar on their birthdays -- Conor, a shepherd-boy-turned servant in a the vaguely Anglo Trunswick; Uraza, a young hunter from the vaguely African Nilo; Meilin, an aristocrat from the vaguely Chinese Zhong; and young thief Rollan from the vaguely Spanish Amaya. When they drink the Nectar, each one summons a spirit animal. 
 This isn't particularly unusual... except that each of them summons a Great Beast. The Great Beasts are legendary creatures which have no appeared for centuries: Briggan the wolf, Uraza the leopard, Essix the gyrfalcon, and Jhi the panda. 
 As soon as the Great Beasts appear, the Greencloaks snatch up the children and whisk them off to safety. The one exception is Uraza, who is found by a mysterious enemy group before the Greencloaks can get to her. The other three must learn how to fight, run, work with each other and their new spirit animals, because their coming destiny is going to be a hard one. 
 "Spirit Animals Book 1: Wild Born" is not really much of a story unto itself. Brandon Mull is mainly introducing us to Erdas, its various lands, the main characters and their Spirit Animals -- not to mention setting up the plot that will presumably flower throughout the books that follow. It's like the first portion of a much longer novel, not a standalone story in its own right. 
 So unsurprisingly nothing is very well-defined yet. It's still not entirely sure clear is going on with the Big Bad Villain and the long-missing Spirit Animals, let alone who the mysterious enemies of the Greencloaks are, or even what the Spirit Animals and their background are. The characters are all promising, and the sheer range of personal backgrounds and different cultures is interesting, but as yet they don't really have much to define them. They can pretty much be summed up in a few words. 
 However, none of this is really Mull's fault -- he packs quite a bit of plot into a very slender book, especially since it's his responsibility to introduce all of this. And his writing style is nimbly and fast-paced, but with plenty of strong descriptions ("The warm, humid air carried the rich smell of jungle foliage, mingled with the salty tang of the sea"), and he adds a lush magical spin to familiar cultures in our own world, even as he deftly drops important facts into the narrative. 
 "Spirit Animals Book 1: Wild Born" is only the first part of a much longer story, and it certainly feels like it -- while the characters and backstory are still half-formed, Mull pulls off this introduction to Erdas nicely.