In the late 12th century, two very strange children came out of an ancient earthwork at the village of Woolpit in East Anglia. They wore clothes of a colour and material never seen before, spoke a language nobody recognised, and were coloured green all over. Later, when they had learned ‘our manner of speaking’, and lost their green colour, they described a homeland which was no place on Earth. The boy died within a year, but the girl grew up and married. Is this a fairy story, or were the children runaways from some primitive tribe?