Is it just a fairy tale, or could a primeval beast lurk in the deep, dark waters of a Scottish lake? Since it was first reported more than 60 years ago, hundreds claim to have witnessed the Loch Ness Monster, while one scientist after another has brought the latest technology to the loch to probe the phenomenon. Twenty-five years after their first, groundbreaking expedition to Loch Ness, NOVA joins two American scientists as they return to Scotland for one last go at Nessie. During a three-week expedition, they use state-of-the-art sonar and sensitive underwater cameras in an attempt to track down and identify the elusive beast. Biologists study the ecosystem of the loch to determine if it could support a large animal. Geologists study its history, looking for clues about what kind of creature might have colonized it, and when. NOVA examines the photographic evidence in the case. And eyewitnesses vividly recount their sightings. Could this legendary creature be real, perhaps a relic from the time of dinosaurs? Or is it a shared illusion—a product of myth, mirage and wishful thinking?