A Cornish bibliophile invites young American scholar Charles Bascomb to his house on the Lizard in Cornwall to investigate a mysterious medival manuscript that he has recently come to possess. Charles, accompanied by his mentor, a well-known Oxford professor, is eager to study the manuscript. He soon determines that the manuscrpt may actually contain a famous lost poem by Geoffrey Chaucer. If true, it would be a monumental discovery, and one that would establish the young scholar's academic reputation. Soon after Charles has made a transcription of the poem, both the manuscript and the professor's car are stolen. A series of strange events ensue, including Charles and the professor making a midnight break-in at a vicarage in an attempt to re-obtain the stolen manuscrpt; Charles being stalked in an eerie, moon-lit church graveyard; and his being attacked in a dark alleyway behind a pub. Along the way, the young American scholar also encounters several beguiling women, one of whom teaches him that Cornish mermaids can be perilous to mortal men. In the end, the manucript is recovered. But does it really contain a poem by Chaucer?