After a world-wide catastrophe (or series of catastrophes), only a few humans survive. They are trapped inside a bunker, with sufficient water, air and food (unvaried though it may be) but too much genetic damage to continue the human race. In hopes of keeping their species going, they start traveling into the past and kidnapping the healthy babies they find. This part of the story is told through the eyes of Pete, a rather stupid teenager who was born in the bunker and views the world of the past through an almost alien mindset.
In their past, and our future, a brilliant statistician named Julie Kahn is investigating the disappearances. This sets her on a collision course with Pete and the future he represents.
A well-written book, but upsetting as all apocalyptic novels are. I wish this had been a little longer and more fleshed-out.