A pilot's encounter with unidentified flying objects led to years of UFO sightings. The Into the Unknown series looks to the skies with The Mystery of UFOs. The story describes dramatic sightings that convinced some people that aliens visit our planet. Skeptics, meanwhile, used scientific tools to raise questions about whether UFOs exist. The text also shows how UFOs created a kind of folklore shared by believers and unbelievers alike. Full-color images help readers see into the mystery. Fast facts, a timeline, and a glossary offer added knowledge. Reading and viewing suggestions show readers where to go to continue their own investigations.