Subtitled ""Investigating a Cosmic Mystery,"" this book brings together the events of June 30, 1908, when something--meteor, comet, asteroid, antimatter, spaceship?--hit central Siberia with a force two thousand times greater than the atomic bomb dropped on Hiroshima. Gallant (A Young Person's Guide to Science, 1993, etc.) investigates this space puzzle with copious references to theories from scientific journals, eyewitness accounts, reports of early investigators, notes from his 1992 expedition to the site, and interviews with contemporary scientists. While there are no answers, he discusses current theories, and relates the occurence to past earth history (for example, the extinction of the dinosaurs) and future events. The book concludes with an extensive list of further reading, with many selections from scientific journals, including several in Russian. While the text is technical, it is thoroughly intriguing; this is especially useful in detailing how scientists work.