A small companion star of our Sun is moving outward from Earth. In another few million years it will turn, heading back toward us to complete

its twenty-six-million-year orbit, passing so close to the Sun and to the Sun's Oort cloud that some of the cloud's billions of comets will be

thrown out of the solar system and others thrown toward Earth. We know from the geological record that the impact of a large body falling from the skies is devastating. One threw a pall of dust and ash over the Earth and killed the dinosaurs.

In this lively, informal narrative, a renowned paleontologist introduces the reader to his and other scientists' research on this controversial theory.