In June 2009 a polite stranger with a German accent spent four days in Sligo, Ireland, methodically deleting every trace of who he was. Then he was found dead on a beach. He has never been identified.

On a clear night in 1978, a young pilot told Melbourne flight service that something hovering above him was not an aircraft. Seventeen seconds of metallic noise followed, then nothing, ever again.

For over a century, shapeless masses of flesh with no bones and no eyes have washed ashore and been mistaken for giant octopuses and hairy sea beasts. DNA finally read the label.

In 1925 a decorated British explorer marched into the Amazon to find a lost civilisation, promising his wife there was nothing to fear. Science eventually proved his city was real. He was never seen again.

A spiny alien that drained goats of their blood terrified Puerto Rico, then all of Latin America. The trail led back to a horror film and a mangy coyote.

A newspaper sensation, a toy submarine, a fleet of sonar boats and a survey of the water's own DNA. Strip away the hoaxes and what is really left in Loch Ness?

For centuries the Himalayas held out a giant with a human tread. Then geneticists asked the hair, the bones and the monastery relics to speak for themselves.

In 1938 a curator picked a steel-blue fish out of a South African trawler's catch. It belonged to a lineage the world had buried with the dinosaurs, and it turned out not to be alone.

For twenty minutes in the clear light of an August afternoon in 1848, seven officers of a British frigate watched a sixty-foot serpent hold a steady course past their ship. Their captain reported it to the Admiralty in writing and never once backed down.

Sailors swore a tentacled monster could drag ships under. Naturalists laughed. Then the carcasses started washing ashore, and cameras finally caught it alive in the deep.

On an October night in 1967, a fishing village watched lights fall into the sea. Police, the Coast Guard and Navy divers went looking. The file is still marked unsolved.

In 2021 the U.S. government stopped laughing off strange objects in the sky and started counting them. What followed was not proof of aliens, but something rarer: an official paper trail of honest uncertainty.