This is a case where the cover and the contents don't quite match.

The cover of Raiders' Ransom shows a youngster -- presumably our main character, 13-year-old Lilly Melkun -- sailing past the top of Big Ben and the towers of Parliament, which just poke out of the water. In the murky depths below, ruined buildings and wrecked cars are dimly visible.

The story by first-time author Emily Diamand is set in 2216, many years after a cataclysmic flood (I assume caused by global warming) set civilization back by centuries. Problem is, it doesn't sound in the book like London is underwater; rather, it's just a bit more swampy in places. In fact, the Thames is still a clearly defined waterway, so the flood couldn't have been too bad, right? Certainly not enough to drown Big Ben, I'm thinking.

That thought kept bugging me as I read the book. That, and the fact that Lilly's sail is red, and Diamand makes it quite clear in the book that English sails are white and raider sails are red. Niggling points like this keep me awake at night.

Don't let it bother you too much, though, because this young-adult novel is well worth reading.

In Lilly's world, technology is banned and people live much as they did in ancient times. Lilly scratches out a living fishing, aided by her rare and valuable seacat (named Cat) who helps her in ways never entirely made clear. She returns home from fishing one day to find her village raided, her grandmother killed, the village's fishing fleet destroyed and the prime minister's daughter, Alexandra, who was visiting an out-of-favor aunt, kidnapped. Worse, the prime minister soon arrives and blames the town for letting raiders take his daughter, and he conscripts the entire population of men and boys for an attack on raider territory.

Lilly, panicked, steals a valuable jewel and sails to London with plans to barter for Alexandra's return. There, she immediately and conveniently runs into Zeph, the youngest son of the Anglian raider who kidnapped Alexandra, and she sets her plan -- well, it's not so much a plan as a good intention -- in motion.

Meanwhile, the jewel turns out to be an interactive gaming computer, still functional after all these years, which is of great interest to the Scots, who still embrace technology.

There are more coincidences than I'd like in this story, but otherwise, it's a pleasure to read. Diamand does a good job developing her two main characters -- Lilly and Zeph alternate as narrator, so readers get both points of view -- and she has begun building a world that is just packed with potential.

The gaming computer, too, is a worthy character here. With advanced AI and holographic technology at its disposal, that little jewel has endless possibilities for use in a world otherwise stripped of electronics.

There is plenty of action, danger and intrigue. There are a host of secondary characters, few of whom are developed much, but we'll see where the future takes them. (Mr. Saravanan in particular needs to return.)

A sequel is in the works, and I hope Diamand takes a little more time to explain the specifics of her fascinating (and damp) new world and the societies within. She has the grist for an exceptional series of young-adult novels ... and I'm already hooked.