This document provides an introduction to the book "Missing Time" by Budd Hopkins, which examines cases of alleged alien abductions. It summarizes three notable sightings by astronauts that were not adequately explained, including observations by McDivitt of a cylindrical object with antennas and a moving bright light. It also notes that while many UFO reports have conventional explanations, a minority of detailed cases from credible witnesses remain unexplained, such as the 1964 Socorro, New Mexico sighting investigated by police and military officials. The introduction establishes that the UFO phenomenon is a serious issue worthy of investigation, regardless of people's theories or assumptions.