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.

On a clear winter morning in 1909 a brand new liner overtook a cargo steamer off the coast of South Africa, exchanged polite signals, and pulled ahead. Nobody has seen her since, and after a century of searching not one plank has ever been recovered.

A civilization of a million people left behind planned cities, covered drains, standard weights and about four thousand tiny inscriptions. After a century of work nobody can read one, and some scholars argue it was never writing at all.

For sixty years the skeletons in a frozen Himalayan pool were explained by one storm and one doomed pilgrimage. Then a genetics laboratory read their DNA and found three different groups, a thousand years apart.

On a Sunday night in 1987, a grinning rubber mask seized two Chicago television stations and spoke gibberish to a city. Federal investigators had every advantage and never came close. Nearly forty years on, not one person has been identified.

Federal and state agents searched his Georgia clinic on 16 June 2015. Three days later the autism physician was found dead in a North Carolina river, and the sheriff ruled it a suicide. His family never accepted that, and a much larger conspiracy story grew out of the case, one that investigators and fact checkers later took apart.