The "Harry Potter" series is not the only book teens have been reading. By the millions they've also flocked to novels by Stephenie Meyer, in which an alienated high school girl falls for the handsome brooding new kid, who happens to be -- a vampire.

The first three books of this series have been phenomenally successful, and a fourth will appear this summer.

In the meantime, Meyer has just published her first novel marketed for adults. It, too, mixes the mundane with the mythic.

"The Host" is set in some vague future, when the Earth (all of it, apparently) has been invaded by a species whose members call themselves "souls" ("parasites," the renegade bands of humans call them) that take over human bodies.

Existing apart from their host creatures as feathery silver ribbons, souls are inserted into the host body via a small slit in the back of the neck made by alien doctors called Healers.

Seekers hunt down the remaining humans to serve as hosts for the kinder, gentler species. The souls retain the memories of the human hosts but take over the bodies, living out the human host's lifespan without the messy emotions and violent tendencies of humans. The result is a "Stepford" society of all peace and no passion.

The central character is a soul named Wanderer, renowned among her species for having lived on eight previous planets, as a spider, a bear, a dolphin.

Unlike other souls who have settled into one species on one planet, she seeks knowledge, growth and adventure, so she is chosen for insertion into a particularly resistant host named Melanie Stryder.

The problem for Wanderer, and the premise of the novel, is that Melanie's consciousness won't be obliterated. She hangs out in this jointly tenanted mind, having conversations with Wanderer, showing her memories and urging her own agenda.

All of this is a brilliant and fascinating premise, and it raises a hundred different questions for the eager reader:

What year is this, and how long has this invasion been in process? How did this come to pass? Where do other host minds go? How do gentle souls manage contentious primary elections?

As a work of science fiction, "The Host" is a disappointment. Meyer's ultimately not interested in pursuing the technical implications of her central idea. The book is narrated by Wanderer, so the only things we learn are the things she thinks about, and she doesn't tell us much.

We barely know what Melanie looks like, let alone the new and improved Earth. The whole first part of the novel is underimagined and is bound to disappoint and frustrate readers with a real interest in her science-fiction premise.

Meyer is interested in the stranger world of relationships. Melanie keeps flashing images of a handsome man, Jared, and one night reveals a dream about her brother Jamie, both of them still human and on the run with Melanie when she was captured.

Rather than turning her information in to the Seeker patrols, Wanderer sets off through the Arizona desert, searching for these two men with the same intensity that Melanie has, finally discovering a hidden compound of renegade humans hiding in caves.

The story picks up at this point, as Meyer describes the ways this group of people have found to farm, feed, clothe, and govern themselves. It's "Survivor" crossed with "The Days of Our Lives."

Meyer is at her best when charting the developing ways the hostile, wary, curious humans respond to the alien in their midst. When the soul, now called Wanda, falls herself in love with Jared, and another man in the compound falls for Wanda, and not for Melanie's body, the result is a fascinating turn on the problem of mind and body.

What is it we love in another being -- body or soul? In this case, there aren't enough bodies to go around for two normal relationships.

But even here, Meyer doesn't push her premise too far. The love between the various parties remains passionately chaste, nothing that would shock her young adult fans.

This science fiction survivalist romance novel may not be rich enough to satisfy hardcore readers of any of these genres, but its mix of adventure and new love on a new Earth is just right to get lost in this summer.