“The Supernaturalist,” by Eoin Colfer. Miramax-Hyperion Books for Children. $16.95.

With “The Supernaturalist,” Eoin Colfer moves from his fantasy world series about young criminal mastermind Artemis Fowl to the grim not-too-distant future science-fiction world of Cosmo Hill.

Cosmo was abandoned as an infant on Cosmonaut Hill and sent to the Clarissa Frayne Institute for Parentally Challenged Boys, which uses its inmates for product testing.

“Cosmo received his schooling from education software, his teeth were whiter than white, and his hair was lustrous and flake-free, but his insides felt like they were being scrubbed with a radioactive wire brush. Eventually, Cosmo realized that the orphanage was slowly killing him. It was time to get out.”

He manages that all-but-impossible feat, skirting death so closely that he is able to see Parasites – blue creatures that suck life. His rescuers are dedicated to killing those creatures.

The science in this science fiction is often shaky and sometimes incoherent. “Of course,” one character states early on. “This is a flora virus. Cellulose would shut it down.” Huh? It doesn’t make sense that a virus made from plant material or modified from one that preys on plants would be shut down by cellulose.

But Colfer’s characters and setting are as strong as ever. So is the story, with plenty of black humor and reverse twists.

“JumpMan – Rule No. 1: Don’t Touch Anything,” by James Valentine. Simon & Schuster Books for Young Readers. $14.95.

This book is goofier but more coherent, a thoroughly engaging first young-adult novel by Australian writer, radio broadcaster and musician James Valentine.

Jules Santorini, 13, has just asked his longtime friend Genevieve Corrigan for a date when a boy with hair that behaves “in a way that usually only lights on a dance floor behave” appears in her room, out of nowhere. As bad as things are for Jules, they’re even worse for Theodore Pine Four, who has arrived from about 3,000 years in the future. Theodore’s fancy new JumpMan was supposed to make him an invisible observer of some fascinating, newly discovered moment – one even better than the discovery of fire. Instead, it has dumped him, all too visible, audible and touchable, into the dullest of eras. And he can’t get back home.

Gen and Jules have to help, with commentary from Jules’ brain:

“Could you stop this please?’ asked his brain. This kind of thinking causes me a lot of pain.”

“Sorry,” said Jules.

“It’s OK. I’m your brain. You’re just trying to make me think about time so you don’t have to think about why you’re climbing these stairs.”

“That’s the trouble with brains,” Jules thought. “They know exactly what you’re not thinking.”

“Good trick, isn’t it?”

It’s great fun, with serious thought bubbled in.