Percy Jackson may have averted a war between the most powerful of the Olympian gods, saving the Western world in the process. But something more dangerous is on the horizon, something old and dark and terrible.

And that power starts pushing its way to Camp Half-Blood in the second book of the Percy Jackson and the Olympians series, The Sea of Monsters. Author Rick Riordan’s writing style is still snarky and fast-paced, and it feels feels a little more polished than in The Lightning Thief – especially since he weaves together a good portion of The Odyssey into his own adventure, but with the modern twist he’s so talented at creating.

For several months, Percy has been attending a prep school, where his only friend is a large, strong but childlike homeless boy named Tyson. But after an attack by monsters, Percy and Tyson are forced to flee with Annabeth back to Camp Half-blood. They soon learn that Thalia’s magic tree has been poisoned, meaning that the barrier protecting the camp is slowly disintegrating. To make matters worse, Chiron has been replaced by Tantalus, who hates the kids and takes a particular dislike to Percy, and Tyson is revealed to be a young Cyclops and also Percy’s half-brother.

But then a dream from Grover tips Percy and Annabeth off to the one thing that can save the camp – the Golden Fleece. Unfortunately, Grover is currently located in the Sea of Monsters – the Bermuda Triangle – and is in danger of being molested by a Cyclops who wants to marry and/or eat him. Unfortunately, Tantalus sends the brutish Clarisse to retrieve the Fleece, and forbids any other campers from going on a quest to find it, on pain of being eaten by harpies.

Shocking spoiler alert: Percy, Annabeth and Tyson decide to go on a quest to save Grover from death (or worse). But they soon discover that satyr-eating Cyclopes aren’t the only threat that lurks in the Sea of Monsters – ancient horrors are lurking, waiting to consume (or transform) the young heroes. Worst of all, an old enemy is also lurking in the Sea – and he wants the Golden Fleece as well.

There’s a hefty chunk of The Odyssey in the DNA of The Sea of Monsters – we have a visit to Circe (whose magical routine has changed a little… but not much), Scylla and Charybdis, and a visit to a Cyclops. However, the core of the story is Riordan’s own, and he creates a lot of stuff for this story that is very much in his own style (such as a Confederate ironclad crewed by zombies), and which works pretty seamlessly with any Homeric homages.

Riordan’s writing is a little more polished in this book, integrating the weirdly mythological with the modern world a little more smoothly (the Gray Sisters and their taxi). And he knows his mythology, as evidenced by the inclusion of Tantalus and his seething hatred of all kids, who is mostly used as an obstacle… and a source of laughs, since his mere presence repels all food and drink.

He also builds up a real sense of darkness and impending disaster, starting with the truly nasty monsters that roam through the Bermuda Triangle area… and building up to to the return of a familiar character, who is planning to use the Fleece for extremely evil reasons. But don’t worry, there’s still a wild, lighthearted side to these monstrous encounters. Let’s just say that centaurs know how to party. And pirates need vitamins.

Riordan also introduces or expands a few characters in the cast beyond just Percy and Annabeth. The most significant addition is Tyson, a kind and gentle boy who is mocked and ostracized by most other kids, especially since he often seems like he has a mental disability. This also leads to some good development for Percy, who struggles with feelings of both love and shame for his awkward, monstrous, childlike sibling – something that many siblings of disabled children sometimes feel. Clarisse also receives some development, since we see her uncertainty and the reason she’s so gung-ho to always succeed.

Rick Riordan was pretty entertaining in The Lightning Thief, but he seems to have hit his stride in The Sea of Monsters. The characters are deeper, the fantastical exploits more intricate, and the threat of the Big Bad substantially more present. And the story ain’t over yet.