Ricky McCormick was found in a Missouri cornfield in 1999 with two folded sheets of capital letters and numbers in his trousers. Twenty-seven years later, the FBI's cryptanalysts and thousands of volunteers still cannot read a single line.

At ten minutes to one on 8 June 1924, a geologist alone on the North Ridge of Everest watched two black specks climbing toward the summit, and then the cloud closed over them. A body came back in 1999, a boot with a foot inside it in 2024, and the one object that would settle the question has never been found.

In April 1943 four boys found a woman's skull inside a hollow tree in a Worcestershire wood. A pathologist proved she had been pushed in while still warm. Within months a stranger began chalking her name on walls across Birmingham, and eighty three years later nobody knows who she was, or who wrote it.

A woman, her employee and a seven year old boy stopped on a Texas back road in December 1980 and watched a burning diamond of light hang above the trees, surrounded by helicopters. All three fell ill that night, and the US Army could never find the helicopters.

Five men left Hana Bay for a morning of fishing in 1979. Nine years later their boat turned up on an uninhabited atoll two thousand miles away, and beside it someone had buried one of them under a cross of driftwood.

He left his blood, his fingerprints, his clothes and his shoes behind, then spent hours inside the house before walking out into the last morning of the century. Japan has been looking for him ever since.

For seventy years we have been able to say the syllables of Minoan prayers and account books out loud. We still have no idea what a single word of them means.

In July 1974 a twelve-year-old girl walking her dog in the Provincetown dunes found a woman whose hands had been removed. It took three exhumations, a laboratory in Texas and a family tree to learn who she was.

At 53 minutes past midnight on 22 September 1979, an ageing American satellite recorded the light signature of a nuclear explosion in an empty stretch of ocean south of Africa. Nobody has ever admitted to it, and Washington still cannot agree on whether it happened.

A three-metre slab covered in an unknown script stood at the mouth of the Singapore River for centuries. In 1843 an engineer blew it up to widen the harbour. One fragment survives, and the writing has never been deciphered.

On a Sunday morning in 1942 a US Navy blimp drifted out of the fog and settled onto a California street. The radio worked, the parachutes were stowed, the doors stood open. The two officers who had flown it were gone, and they have never been found.

A crater in the Turkmen desert has been burning for around fifty years, and millions of people know exactly how it started. The problem is that the story does not appear in a single document, and the geologists who worked there tell it differently.