The Vesuvius Prophecy — Greg Cox

4400 taken, 4400 returned.
With no memory of where they've been.
And they haven't aged a day.
Some have returned with startling new abilities...

Eleven-year-old Maia can see the future, and she's never wrong. So when she has a vision of Mount Rainier starting to erupt, the National Threat Assessment Command takes her warning very seriously. But to track down the unknown returnee who may trigger the volcanic eruption, NTAC agents Tom Baldwin and Diana Skouris must uncover the astounding truth behind one of the greatest unsolved crimes of the twentieth century....

And they've got competition. Ruthless enemies are working against them and somehow managing to keep one step ahead of the desperate agents. With the future closing in on them, Tom and Diana must foil a lethal conspiracy -- before Seattle and the entire Pacific Northwest go the way of ancient Pompeii.