If you just can't get enough -- pirates, that is -- Kai Meyer's new YA fantasy series will feed your fix and keep you tolerably entertained while you await something more substantial. Nothing mindblowingly profound: Pirate Emperor is simply a rip-roaring, swashbuckling adventure with unlikely heroes, cannibals, ghosts, sea battles and even a god or two.

But if you haven't read the first book of The Wave Walkers, Pirate Curse, you may find yourself at sea amongst numerous plot threads, a cast of thousands and a completely unfamiliar system of magic based on ... mussels. Fortunately, shellfish are merely the tip of the iceberg where the mysterious abilities of polliwogs are concerned.

Don't be alarmed -- Pirate Emperor is not about Shellfish of Doom wielded by tadpoles. Polliwogs are very special humans who can, among other things, walk on seawater. There are just two of them left in Meyer's alternate Caribbean world: Jolly, a teenaged pirate named after the pirate flag, and Munk, a sheltered boy of the same age. Being a polliwog is not all fun and games: everyone seems to want to kill or use them. This includes even the apparently benevolent denizens of floating coral city Aelenium, for whom the two polliwogs are heroes prophesied to close a breach at the bottom of the sea through which an ancient evil is seeping. Or is it? Munk swallows the story and embraces the responsibility -- and glamour -- of the quest, but Jolly wants nothing more than to find the pirate comrades she lost in the first book.

However, the climactic scene at the Crustal Breach is clearly designated as Book 3 material. Pirate Emperor, suffering from middle-book syndrome, builds up to the forthcoming climax with some surprising revelations, but overall seems more like a set of somewhat loosely related but page-turning adventure sequences. From the race across a burning bridge that opens the book, to an unscheduled trip inside a giant whale's belly, to a gladiatorial contest between pirates, Pirate Emperor is breathlessly paced and often cinematically described.

At the same time, the book is marred by occasionally awkward translations and jarring jumps between stories in which, by the end of the book, little has been resolved. Like Pirate Curse, it doesn't explore the pirate cliches it uses, and an emphasis on splashy magical action shortchanges characterisation. The growing tension, sexual and otherwise, between Jolly, Griffin and Munk as each tries to decide where his loyalties lie is interesting, but the adults remain largely flat and interchangeable. Given that these include a pirate princess and a dog-headed man, that's a shame.

Those looking for novels with historical pirates are better off with Celia Rees's Pirates!, and those seeking more character-oriented fantasy should steer towards Tanith Lee's Piratica. Kai Meyer's Pirate Emperor works best as action fantasy that uses pirate tropes -- parrots and all -- for a breezy, quick-paced summer read.